There are no unique problems on the current version so far.
Actually, this is more an issue with Android M/Xposed than with MaxLock. The reason lies in Settings app using another SELinux context than most if not all user apps, disallowing it to read MaxLock's preferences. However, this would be needed for MaxLock in order to operate.
MaxLock isn't able to correctly lock chat heads, as Facebook doesn't use normal activities for it, instead it draws on top of other app (because it's an overlay), which means even when MaxLock appears, the chat head is still on top of it and accessible.
If a user presses the "Back" button, the lockscreen exits and the underlying app gets exposed. This issue is caused by SwipeBack2, another Xposed module, which hooks the same methods and therefore stops MaxLock from working correctly.
The only way to remedy this is to not use the mentioned Xposed module.