I did a pretty clean installation and stumbled on the following Alert in SCOM 2016 TP5:

Database connectivity is lost, with details:

The EXECUTE permission was denied on the object ‘sp_help_jobactivity, database ‘msdn’, schema ‘dbo’

The following SQL did the fix: (Data Writer Account)

use msdb
Grant Execute ON OBJECT::[dbo].[sp_help_jobactivity] To [HQ\OMDWWrite]

See you