Export Issue: Error retrieving frame X at time X from file X, substituting frame X

I've been frustrated beyond belief with this project I've been working on (it's had a variety of problems...) and have now run into a final straw scenario. Delivery is tomorrow and I do not know how to deal with this sudden error.

Earlier in the day, I exported a few sample clips for the director, no issue. Now the entire project, including those same clips, is failing to render. NOTHING HAS CHANGED.

I don't know why the sudden breakdown. I've never run into this issue before.

I've followed the steps in this post that seemed to solve it but it's no use for me.

Moving it locally didn't correct the issue.

Creating proxies of the newly coloured footage I'm working with returned an error on all but 9 of 24 clips. All the same issue: can't retrieve frame, etc.

I've updated Media Encoder, Premiere Pro v.25.2.3, and my NVIDIA 1060Ti to their latest, and still nothing.

Please, please help. This "for fun" project is going to kill me.