I’ve come across files that were changed by a REST call from Mendix. The REST call added some extra information to the file which corrupted the file.
Can you check if the content of the file is still the same, retrieving it via Mendix and Postman?
I have exactly the same issue. Did you log a ticket for this with Mendix?
It runs indeed fine in the cloud but it seems that is not the differentiator for this issue. I just increased the REST log levels to TRACE in the cloud (on TEST) and then I also had the issue. Putting the log levels back to INFO resolved the issue.