Do you have enough memory on the server?
I believe I have enough memory, 8 GB
The symptoms happen with only FMS running.
With Yosemite, I ran FMS 14 + FMPro14 + Mail.
Have you restarted the server? I've seen that widget problem fixed with a server restart.
If that doesn't work then try uninstalling and re-installing FMServer according to the FMServer getting started guide: https://fmhelp.filemaker.com/docs/15/en/fms15_getting_started.pdf
I have restarted the server several times.
Restarted the server mac mini.
I have just uninstalled FMS15.
I renamed Library/FileMaker Server folder
Same problems happen.
With only FMServer_Sample file loaded onto the server.
You may want to do a permissions repair on the drive especially since you just upgraded the OS. Worst case you may want to do a full blank install of the OS.
What you are seeing is not typical or normal.
You don't have OSX Server running do you?
I do not have OSX Server running.
I have just reinstalled FMS15, after deleting FileMaker Server folder.
I have renewed my SSL Certificate.
It is still very slow.
I have not yet seen the Widget message.
I will investigate the permissions repair - thank you for the suggestion.
El Capitan no longer does Permissions Repair. There is a new Disk Utility.