Error "decrypting file would take too long" despite same MAXTIME

[AnLAdmin]

I wrote a test to test a function where I use .decrypt(). In this test I use the same MAXTIME (0.5) in encrypt as in the tested function. Despite that I get sometimes "decrypting file would take too long" error. I tried also to encyrpt with 0.5 and decrypt with 1. I also sometimes got the error. With 0.2/0.5 This seems to work. At least until now. Why can this happen? And what is the best practice for the MAX values?