"Premiere Pro !" Error when rendering

I'm getting the attached error ("Premiere Pro !") when trying to render a 1h30 timeline in H.264 (very helpful error message btw...). Prores HQ renders fine. I've cleared the cache, restarted the mac, reset and rolled back the app, same result. This used to work fine with similar size projects. Only change / update I am aware of since last successful H.264 render was the Apple 15.7.2 update. 

Premiere Pro 25.6.3 (build 2), have tried 25.6.2 as well, same error

MacOS Sequoia 15.7.3

Macbook M4 Pro 24GB ram

Source drive is an external thunderbolt nvme ssd. 

Destination drive is the internal ssd (have tried other external ssd's as well)

Any ideas?