After a glitch performed via a add-on, or else. You can have a item stacked over 64 (like 65, or 99), and when you select it on inventory, the game crashes,(it's maybe not that but it's my gess) and on reload when opening the ingame esc menu, it causes a several lag(watch screenshot), that maybe is infinite. (i everytime Alt+F4 because i can't do anything.)
Please help fast beacause it was the case before, and my only way to fix it is to redownload minecraft, and i don't want to, andif it's the case to somebody else maybe he/she too.