It sounds like something changed at the system or driver level rather than Action itself. Recording MP4 at 360 FPS is extremely demanding, and if hardware acceleration suddenly became unavailable, that would explain the corrupted files and missing thumbnails. First thing to check is your NVIDIA driv...

Since you’ve already updated, reinstalled, and checked network and firewall settings, it might be an issue on Action’s side with Twitch integration. Using a manual stream key for Twitch is a reliable workaround in the meantime, and you could also check if Mirillis has any beta updates or support not...