I have that same problem, and I've been told that the cause is off axis torque. Some people call it OAT. It's caused by rotational forces not through the center of the disc. Think about a record player. If the hole in the record is off-center, then the disc will not rotate smoothly on the record player. That's an example in two dimensions. If you move to three dimensions, you have trouble with not having smooth motion in the vertical direction.
Here's some advice from another board on how to reduce OAT:
The two biggest motions that contribute to OAT are wrist roll (either under or over) and lack of plane preservation with your arm and shoulders on your follow through. Rolling your wrist over (your palm is facing the sky immediately after the hit) and following through on a lower angle than the discs' angle at the hit cause discs to act more understable. The opposite cause discs to act more overstable. The former is a much more common problem.
OAT, when intentional, can also be used to control a discs's flight and shape lines. Say you want to have the disc flip from hyzer to flat, glide a bit, turn over, glide farther and then fade. You can throw a disc like a beat DX Eagle-X on a hyzer, but finish on an angle less than the hyzer angle. Controlling how much of a difference there is between the angles will allow you to control when the Eagle goes from straight to tracking right. Depending on how beat the Eagle is, the disc will either continue tracking right, fade back to straight and glide a bit, or fade back left. Once you get good at these types of shots (sometimes called roll curves), the negative effect of choosing the wrong beatness of fairway driver will have a small impact (perhaps 10') rather than a large one (30'-40' off for choosing the wrong mold).
Roll under can be used effectively too. Say you have a shot that's kind of short for a midrange, but there's a stiff left turn at the end. You can throw your mid with less hyzer than normal and roll under (or follow through on a higher angle) and the disc will either hold a hyzer the whole time or fade out earlier/harder than it would on a normal shot.
One of the easist ways to get roll under out of your throw is to practice throwing your most understable plastic on pure hyzers. Start off short and lengthen how far you throw, avoiding letting the discs flip up from a hyzer at all. Eventually you'll get the feel for how to control the wrist roll. Your slower discs will fly farther and be much easier to control and the speed you gain (or stop losing from OAT) might make the best longer range disc for you more obvious. You'll start seeing lines you never knew existed, using discs for shots you never imagined would work (I threw a flippy Gazelle ~350' into a headwind a couple weeks ago) and you'll amaze people because it starts looking like your discs are remote controlled.
Wobble, OAT and Flutter are all the same thing. Personally, I like the term Flutter the best. It means you are not releasing the disc clean and flat.
Flutter can be due to a weak grip but most often it is due to not releasing the disc flat enough. Think flat, like parallel to the ground.
Most forehand shots naturally have a degree of flutter (or a lot of flutter for forehand newbies). Most decent backhand shots come out pretty flat. It is just the bio-mechanics of the disc and the human body. Don't blame yourself, it is the way you were designed. But with practice you can work to minimize flutter.
Flutter costs your shot distance and stability. So your shot will go farther and hyzer more when you diminish your flutter.
Don't worry about spin or speed. Concentrate on flat, clean and smooth. If you can do all that then add in balance and follow through then you will be way ahead of the game. Heck, you will be good.
Go read disc nut's post, he hits the nail on the head in one sentence. There is very strong evidence that the primary cause of OAT is insufficient spin to match the forward velocity of the disc. Think about your disc as a flying wing. What we know is that a disc that comes out with no spin has one speed at which it will fly correctly without tumbling (if you look through the archived threads here, you'll find the article posted). Putting it simply, spin stabilizes the disc by distributing the forces on the disc around the edge of the disc.
To test this theory, do a couple of experiments. Go out and throw your discs on a windy day. Down wind you will see less OAT. That is because the disc is traveling slower relative to the wind, physically, the disc for all practical puposes is traveling slower relative to the air around it. So, if you have inadequate spin for a faster forward speed, the disc will still fly without OAT because it is flying at a relatively slower speed. Up wind throws will show greater OAT since the wind coming at the disc makes the disc appear to be traveling at a greater velocity, again relative to the air through which the disc is traveling. There simply isn't enough spin on the disc for it to fly stable.
This OAT relative to wind direction effect will occur no matter what grip, release or style you use, that is, it shows that the issue isn't some strange release angle or other factor. The reason why players see things like disc angle, wrist rotation and a loose grip cause wobble is because all of those things, in one way or another, result in less spin on the disc. All of them take directly away from...
Solution, more snap to put more rotation on the disc. Now, many have written about snap and somehow no one seems to be able to tell a player exactly how to improve their snap in a consistent way. Once you know it, it becomes obvious, but getting there can be tough. One thing that will help is to think about your throw, instead of throwing to get high forward velocity, think about a throw that puts more spin on the disc. Just that mental transition can do wonders. Yes, to throw 600 feet you need to get high forward velocity, but to get 400 feet, you don't need it, and lots of spin puts you there way better than lots of forward velocity. That is. way to many people get too caught up in throwin' that disc hard. Think snapping that disc hard instead.
BTW - the reason, IMO, that you see more OAT on forehand throws is that the arm structure lends to a very fast forward motion without the ability to put snap on the disc, in a forehand shot. In that shot, you are working almost exclusively with your wrist to put snap on the disc and you are working with a contrived snapping motion i.e. it is directed. On a backhand snap you are using your arm much more like a whip. The physiology of the arm lends itself to a motion that whips your wrist at the hit... if you do it correctly that is. In one case you are whipping a stick with a 5 or six inch rope on the end, in the other, you have a two foot piece of rope you are snapping since your forearm physiologically becomes part of the snap. Think about it like this, if backhand players could adjust their throw angles in such a way to eliminate OAT as they get better, why wouldn't a forehand player be able to do the same, unless there was some basic difference in how the disc travels through the air? The idea that it is angle of release doesn't fit the wide variety of angles that players of both ilks utilize.
One last thought, go look at video of tournament play, especially on upshots; you can look at discgolfmonthly.com. You will see many many upshots come out at all kinds of disc angles, nose up, side down, nose down, etc. None of them come out with OAT. That is because all of them are traveling very slowly, with lots of spin.
Work on a smooth release.
Practice. Practice. Practice.
Go to an open field and throw or putt.
Whichever is wobbly...
Smooth it out. Try snapping a hand towel.
Release discs with snap, then follow through.
Stand sideways to your target and rotate the hips.
Practice more. It comes to you with practice...