Like I said, I haven't used mini.comment, but having both gc and gcc mapping may cause problems. If I remember correctly, in these situations, neovim waits after receiving gc command to figure out if you are trying to execute comment last or gcc with comment line. Depending on timelen (or timeout, forgot the exact name) setting the command you actually execute will defer based on the key pressed/not pressed after gc.

Also, if gc is mapped to comment last, and there was no last comment action performed, it might do nothing (maybe check the readme to be sure). So maybe try changing the mapping to see if that helps.