I got the next message from SF :
Hourly limit exceeded for processing workflow time triggers.
I read that the limitation for Enterprise Org is 1000 per hour. ( https://help.salesforce.com/articleView?id=workflow_limits.htm&type=5 )
When I entered to /services/data/v45.0/limits From the workbench I saw a very strange thing :
but when I went to Setup => Monitor => Time-Based Workflow, I saw 196 rows but none of them are Time-Dependent Workflow. Its Immediate Workflow.
So I don't really understand where it's coming from and why I see limit of 50 at Workbench while 1000 in SF Limitation Docs...
What I didn't understand here correctly?