What is the ph of the tank? glass cats thrive at 6.0-7.0. They are usually wild-caught and not as likely to adapt as tank-bred fish. Mollies and other livebearers thrive at 7.5 and up. Also the glass cats are very shy sedate fish that could easily be disturbed by any semi-aggressive mollies, and unfortunately a lot of mollies are bullies.
I have always wanted glasscats! 20 years now ive been wishing my ph was lower.