Limits on Expression size?

I have a Microflow return expression which is very large (parsing a long enumeration list for data import). When I get a certain way through inputting (typing) the expession the Modeller (6.9.1) consistently crashes (just dissappears). Is there a limit on the size of expression that could be causing this? Any ideas?

Many thanks.

Thanks for your answer. However I have decided to do this a different way which eliminates the problem.