version 3 to 4 anomaly - tiny notes

I have a string orchestra score that was just converted to version 4.1.1 All the parts are fine except for the cello part. The notes on the cello part are miniscule. I've tried everything I know to change it - at first it insisted on making most lines a single measure long (and no, there was no visible line break icon), I've tried reducing the number of pages, Nothing changes the notes from too small to read. I tried deleting the cello part and recreating it, but it sill appears in tiny notes I wouldn't inflict on my basest enemy. The bass part, which is similar to the cello part in content, is normal size. What can I do? Everything looks fine in the score, just this one part is wonky.

Well I wanted to send you the musescore file, but can't persuade the space below to take it!