Thank you for the feedback!
This prompt vanishing glitch has to do with my interaction manager. I'll make it a priority to patch this once I review the code. I'll also add the sound effect preview, I totally forgot about it while rushing to finish the game's audio.
For the shop, I made 3 slots with different pools and one that is always a heal. The third one can spawn any upgrade, which is why there can be duplicates. I didn't make it very clear in game, but upgrades are stackble (except for slash damage, which stops spawning once you buy it)