I'm glad you sorted that out. Couldn't you make the tilt shift with Lightroom (Gradient based corrections -> blur and maybe Lens-Corrections) ?

I hadn't looked into that...I will though. That would make everything much easier.

Just FYI, the problem seems to come from the way Photoshop writes the image metadata. It ends up with a file size of 1280000x720000 instead of 128x72 like my LR files do. I'm guessing this causes some sort of memory overflow after a bit of attempting to export?

Ii might be. Since that's an adobe issue (Photoshop export into LR) I cannot say what's the cause. But it's a shame there are such incompatibilities in the same family of software anyway (I already experienced similar problems).