Hello,
For some reason, when I open a WAB app that use ArcGIS for server 10.3.1 services, it can load any layer and that is because the services stop working.
When I check ArcGIS Server service and restart the service I got the error 1069: The service did not start due to a logon failure.

I login to the service


It start working again fine after login. one or two days working fine, suddenly i cannot see layers in my WAB app and the reason is because again, Server service is not working, I need to type arcgis password again for service runs correctly.
Why is my server service login out? why is it not working fine? anyone has any idea what could be happening to ArcGIS Server service?
ArcGIS Server 10.3.1
Windows Server Enterprise without Hyper-V SP2

Thank you,
Diego Llamas