I think this combo counter resetting glitch is still pretty new and unknown, but basically what happens is if you use a bomb in a combo, and also block the bomb yourself, Joe’s hits vanish from the combo counter.

So if it’s just Joe by himself, it can make the combo counter disappear, making it look like a reset (but it isn’t, it’s still a legit combo). If you use other team members and then the bomb blocking glitch, you can make the combo counter suddenly drop, which is what happens after 100 hits in the first combo.

Iso wrote up some more notes in the description. Another fairly (i think) unknown thing was using the same assist twice in one combo.