I am having what I think is the same problem on my iPad mini. If I unlock Enpass, then try to use it to enter password information on some app, the blue window to enter the Enpass master password is shown. I have tried using the split screen so that both apps (Enpass and the app that needs the login info), are open and visible and that doesn't help. The security settings don't make a difference. It's extremely tedious to enter the master password on an iPad mini, so I don't want to do it more than should be needed. After I enter the master password yet another time, the login works as it should.
I am using the free version of Enpass but had (past tense) planned to get a paid version because I really like the program. With this flaw, I will wait or skip it altogether. Please fix this.