sharepoint 2013 workflows not working: request time out

Hello!
Our onpremise Sharepoint 2013 servers's all workflows are stuck. We have a test workflow, and if I start a new it stuck at "started" state. After a time it hangs and goes to "suspended" state with an error:
"RequestorId: 809e20a5-9578-bbe8-0000-000000000000. Details: An unhandled exception occurred during the execution of the workflow instance. Exception details: System.TimeoutException: The HTTP request timed out after retrying for 10.00:00:00. at the following location: Microsoft.Activities.Hosting.Runtime.Subroutine.SubroutineChild.Execute(CodeActivityContext context) at the following location: System.Activities.CodeActivity.InternalExecute(ActivityInstance instance, ActivityExecutor executor, BookmarkManager bookmarkManager) at the following location: System.Activities.Runtime.ActivityExecutor.ExecuteActivityWorkItem.ExecuteBody(ActivityExecutor executor, BookmarkManager bookmarkManager, Location resultLocation).
I checked the admin center warnings, service states, event logs, everything’s look okay (for me). Maybe irrelevant, but the problem started (as far as I know) after one of the college renewed the SharePoint worklog manager certificate. The certificate is self-signed. I also cleared the sharepoint designer cache, ran Sharepoint 2013 product configuration wizzard, to repair SharePoint environment. Ran iis reset, did server restart.

I have almost zero experience with SharePoint, so please give detailed requests and instructions if you need any more information. Any help appreciated.

Thank you.