how can i fix error fffffff?

for context my game has been crashing usually when doing sort point of a mission? like when I'm in free roam there's no issue at all but then when i go in to missions at some point it just crashes and tells me ^error FFFFF^? I've tried to look up tutorials but i have just seen ppl talk abt modders? now I'm not quite sure they're talking abt online but this issue just started for me. literally worked fine last week pc gaming at its finest.