Stack overflow in proof with ~500 lines.

I have a document with around ~1500 lines. In one proof, I am unable to progress after about 500 lines due to stack overflow.

The message I get is "Anomaly "edit_at 1328: Stack overflow..""

See the attached document, I assume it's nothing specific about the proof but rather the size; or something like that. The error happens in line 1041/1042, when I try to edit something there.