It's possible that the log writer wanted to fseek to the end of the file and write something, but the target pointer value was somehow corrupted. Depending on the OS, the file might end up having a fuckton of zeroes in the skipped part.
It's a crash log, not an error log. It's probably dumping the entire memory stack to text instead of a bin dump every time it crashed. I would also suspect the crash handler is appending to the log instead of deleting old crashes and just keeping the latest. At several dozen gigas of RAM it would just take a couple of game crashes to fill up the 300GB.
It happened to my cousin awhile back with Photoshop. She’s a professional photographer and it shut her down for a few days. I found it pretty quickly and an update stopped it from happening. It wasn’t removing temporary files and totally filled her drive up.