Just to quote the ones I've already listed in the release thread:
EDIT: You also can't run through the gap in the bombs at the end of Special Stage 3, costing me the emerald. I wasn't expecting that.
I'll list the others so they are least documented:
- Double rings in Emerald Hill Zone 1 near third starpost.
- Emerald Hill Zone background cuts off due to larger screen size
- My score clocked over 50,000 during the special stage tally and I was awarded the 1-up during the level's title card loading; way after the score had clocked over.
- Priority on the Chemical Plant Zone flipping floors is wrong; you go behind them when you should go in front.
- Screen unlocking on bosses happens way too early. You can avoid seeing Eggman blowing up entirely if you're quick, which feels weird.
- Aquatic Ruin Zone 2 has some strange priority issues where sometimes I end up in front of foreground pillars and undergrowth. I presume this is a path swapper issue.
- Monitor icons (contents) have low priority when they should be higher. You can't see the contents of a broken monitor when it's behind something.
- Pressing jump when coming off of a flipper or spring will transform you into Super Sonic, which doesn't feel right.
- You can't get enough height to get on top of the first loop in Casino Night Zone 2 as Sonic. You used to be able to from the slope and red spring beforehand.
- The collision detection is a lot stricter compared to the original in that I can die from being squashed a lot easier in places. This can be seen easily in Casino Night Zone if you go onto an elevator and then move to the left edge of it as it rises.
- The camera doesn't move up at the end of Hill Top Zone 2, which causes the focus to be in the wrong place.
- The 3 boxes right of the invincibility in Mystic Cave Zone rotate the wrong way around.
- The Crawlton badnik's range is now too long, causing him to attack you from a much longer distance and become disjointed from the rest of his body.
- Super Sonic's underwater palette (in Hidden Palace Zone anyway) is broken. It's neon green with a blue forehead.
- Beating the new boss as Super Sonic causes him to blow-up indefinitely. I don't think this was intended and it can also cause the player to be stuck in an endless loop because Eggman can no longer be destroyed.
- The background for Oil Ocean Zone is way too low when you are at the top of the level. You can barely see the sun and clouds.
- I can get shot by an Octus after getting into a vacuum tube, which negates the vacuum tube. never used to happen before.
- It's easier than before to cheat your way under the oil in Oil Ocean Zone. You can't spindash but there's a lot of leniency to just keep jumping to stay alive.
- One of the fans in the middle of the long slide (after the middle starpost) in Oil Ocean Zone 1 is the wrong type; it should be facing left, not facing up.
- I randomly accumulated "2" points during a level transition.
- Switches in Metropolis that you could normally trigger by running over them no longer act as such and instead require a jump onto them instead.
- Multiple rings in the same place in Metropolis 2. There are 4 rings behind a row of 3, making 12 in total.
- Same issue as Sonic 1 2013 - A 1-up jingle can be interrupted if you collect a few rings or lose them while it's playing.
- The large black pistons are always open instead of closed when you encounter them, which makes you wait for a few seconds each time, instead of running over them.
- The bass line in Sky Chase Zone has a drum beat that is off, timing-wise. To anyone who's listened to Sky Chase enough, it's quite obvious.
- Turtloids don't go into their fired animation frame after they fire. I didn't know if any of them were going fire again or if they already had because of it.
- Jumping out of the door in Death Egg Zone into Silver Sonic's arena shows him floating in the top right.
- You can spindash through both doors where Eggman is waiting, making him teleport in front of Sonic running away.
- There's a whistling noise in the background of Casino Night Zone's part of the credits tune. It's out of tune and it runs that section of the track.
That's all for now. Also to note, I'm not finding and listing these things to harm the release; I'm doing it to support the release and ensure it becomes the best version possible.