This little bug keeps happening whenever i convert more than 2 materia within in a short time frame.
It'll stop the animation and grey out all actions/ abilities on ur hotbar.
It'll prevent you from doing anything and even quitting/ logging out of the game.
The only way i found out to get out of it was to switch areas or get killed by a mob. If this happens to you in your fc's house then it's kinda gg.. Unless you hard boot your game.
It's probably lag or something but when it happened to me, everyone around me weren't lagging , fc chat was fully in sync and damage recieved from attacks were spot on.
I only noticed this after the most recent maintenance.