This is going to seem remarkably silly however it has proved to be a reliable and consistent solution.
STEP BY STEP:
1.) Before opening SignagePlayer open another application and type your login username. COPY THIS.
2.) Open SIgnagePlayer, Enter your PASSWORD FIRST.
3.) Paste your Username.
4.) DO NOT LOGIN, let it sit for one minute. (sounds superstitious but login immediately crashes player, waiting gets you in.
5.) After your wait, Login.
6.) Congrats.
This is weird, but it works over and over. Any deviation from this ritual results in wanting to punch your fist through the screen. I've tried deviating from this and it never works. Following this quircky procedure logs me into every new player on the first try every time.
Hopefully this can be examined by the Development team.
Thank you and happy Android log-ins!