Last night I installed usermanager 4.16 on routerboard.
default customer of admin & no password
created user demo demo
All worked fine. Inside usermanager web interface I changed admin password from blank to admin.
Still worked fine to access userman

Today when try to login, nothing happens with admin admin.
No messages, just erases entries on login screen.
With incorrect entry is give invalid user error.
I checked with terminal and customer name is "admin" and password is "admin"
Logging into hotspot still works fine with demo demo

The hotspot user database is evaluated first. Check "/ip hotspot user print detail". Is there an user "admin" there also?

There was not a user in the hotspot named admin.
But I looked closer this time under /tools user-manager customer print & noticed that the only cusomer "admin" was disabled. I enabled it and it works fine.
How could it have become disabled?

In the CLI In the User Manager web interface, click (check) the square next to "admin" and move your cursor over the edit button. You will see a disable option.

I also have an "admin" customer, but it is enabled by default. V4.16.