tex2LyX error

[Hal Kierstead]

All - 

I have a 1227 line LaTeX file that compiles fine. I would like to import it into LyX 2.3.7. Every time I try the import ends at line 543. This is just before an \end{proof}. After adding the missing \end{proof} the shortened LyX file works fine. 

I have tried importing other LaTeX files without problems. I have also tried restarting LyX. What could be happening?

Thanks,

Hal