I encountered this problem with a customer where one of our workflow heavy applications stopped to function .
The error I got within ULS Logs look like
00000003-0000-0ff1-ce00-000000000000 trusted provider is missing
Turns out it is a security change to the IIS Application for the “Workflow Management Site” where the Authentication provider included
Asp.Net Impersonation Enabled Along with other changes to that IIS application .
This customer is using SharePoint 2013 Enterprise on premises with NTLM only in a windows integrated mode , no SSL .
After narrowing down the issue to “Authentication problem” I did setup a new WFM with OOB configuration.
Asp.Net Impersonation Disabled
I have checked all those settings below this will fix this issue after you restart the application pool.
Best of Luck.