Recently, I came across with the following issue, I Opened the Search Service Application in one of the Servers in the farm, and when I click on Content Sources I was getting:
The search application ‘XXXX’ on server XXXX did not finish loading. View the event logs on the affected server for more information.
After spending some time to fix the problem I found the following command:
Psconfig -cmd secureresources
It takes a couple of minutes to finish it.After doing this I was able to enter again to Content Sources in the Search Application
Hope it helps!