Java Script done in Pro, works in Pro and MS-Edge but doesn’t work in Adobe Reader?

I have to modify a PDF-form a coworker created some years ago. Two pretty big if-then-else scripts (~ 450 lines) used to work well. And they still work well if you use Acrobat Pro or MS-Edge (sic!), but fail with Adobe Reader.

I’ve changed the huge if-then-else to an array – again, works fine in Pro and Edge – but not in Reader...

Any Idea what might go wrong. Aside from the size it is a simple if-then-else script, nothing special about it. Other JS in this very form work fine with Reader too …

Additional Question: Actually the two scripts should be a big one. I thought, when changing to an array I could combine them in a single field. But there seems to be a limit to the number of lines allowed in Acrobat. Though there is no error, values at the end of this array are simply not found …?

Thank you