Thank you for playing the game! I watched your playthrough on stream, and I agree with the criticisms you made. The HP mechanic was a tough balance. I struggled with coming up with ways to make the game feel fair while maintaining the atmosphere and style of play I wanted. I wanted the game to be challenging and suspenseful, and require a degree of caution and patience from the player, but in the end I think it just came out punishing. I've watched / listened to about a half a dozen people try my game out so far, and the main character's fragility has been the first and foremost complaint of every one who played. In my head I suppose I saw this game a bit like a shoot-em-up. You've got the fragile main character who dies in a single hit, and a bomb (the potion) that you can use as a panic button to get you out of a tough situation. But I guess I forgot that in those games you typically get multiple lives.
On the stream you brought up that it would've been a good idea to add a quit / retry menu instead of having to completely restart the game, and that's actually a really great idea. Where to put the player on reset was a tough decision as well, but the full restart was mainly a product of time constraints. By the end of the jam I was just rushing to wrap everything up to be in a playable state. The game does need some more QOL features, I agree, but I simply didn't have the time to add them before the initial due date.
The UI graphical bug you experienced was caused by putting the game into fullscreen. Unity's UI system is a bit strange in that each element can be given an anchor point + an offset position that allows it to render relative to that anchor point, and by expanding the screen size those anchors were moved around as well. So the Z and X button icons, for example, were anchored to the lower right of the screen and given a small offset. The game was only meant to be played at a 900x600 resolution, so when the screen got bigger the bottom right shifted to being in the black void and the icons went with it. The hearts in the health bar were also a casualty of this problem.
I noticed you also had a glitch where the main character went invisible after getting hit, and I believe this was a case of me doing some bad code. I think it's caused by the player getting hit while still invincible somehow, and the routine that handles the blinking animation ends up running twice and blinking the player's sprite out of existence for a bit. I had run into this a couple times while playtesting and it would've been a very quick and easy fix, but I just forgot about it. Whoops! :S
I'm sorry for the longwinded response. I appreciate the feedback, and I'm glad to hear you enjoyed the game (at least a little)!