Hi, the reason the PIN is not asked for in 100% of cases probably is that in the latest app versions the app gets locked 10 seconds after you leave it. If you re-enter it in less than 10 seconds, no PIN is required.
We are planning to extend options for app locking, hopefully in summer 2017.
However, if your app lock settings got lost after the update, we are very sorry. We would really appreciate, if you could let us know from what version to what version did you update when it happened. Thanks!