An hour?! Thanks a lot for sticking with it that long! 😄 I'm really glad you ended up enjoying it that much.
About the coin counter, that actually sounds like something I should double-check. I haven't seen it reset like that during testing, and it's one of the earliest systems I implemented, so it has had quite a lot of testing. The only thing that comes to mind is that maybe some of the coins were being spent on upgrades without it being immediately obvious, but I'll definitely take another look at the code. Thanks for pointing it out!
And I totally get the disappointment with the last speed upgrade. It was originally supposed to open another branch of the tree, but that part didn't make it into the jam version. I had a fourth character planned, along with a few more dungeons and some other upgrades, but at some point I had to stop adding things and focus on actually finishing and balancing the game.
Thanks again for playing it all the way through and for taking the time to write such a detailed comment!