Game is fantastic. I've also left (the same) feedback on the Discord.
If your high score goes over 32768 (makes sense, it's the max for a 16-bit integer), saving to the leaderboard stops working, and the results screen also never shows. Additionally, any scores over 9999 don't display properly on the game screen.
I played again, keeping track of my score so it didn't roll over 32768. I got to the results screen, but it no longer recognizes that you set a high score. The bonuses also rolled the number over in a weird way. So if the score is bumped over 32768 at any point, scores aren't saved.
When (and if) this gets corrected, my highest score has x1807 slimes cleared, 33m15s, and score of around ~40,000.
Until then the above screenshot is probably the closest I've gotten to the (current) maximum possible score. I dare anyone to beat it! :D