if there is no changes to your end point. I would request or suggestion you to verify the exported package and try to verify the json file. Do you see any “/” is appended in your endpoint.
Also enable the debug log and test the service before export from lower environment and after importing the same package to higher environment.
if you don’t see any progress in your finding , I would suggest you to create support ticket for temp work around fix. Maybe your endpoint might malfunctioned.
Work around is already you doing by enabling and disabling the API.