http-enabled is set to false and we are also forcing an https connection via ONTAPI. Unfortunately, I cannot just try what happens if we enable http on these systems. Do you have an iday why this could help?
The error "not authorized for that command" turned out to be an issue with the role which was assigned to the user. The role has been deleted and created again with the same(!) credentials. Now it is working. Note that the original role was working with 8.3.2 before.
The other error "HTTP POST - Authorization failed" still not solved. Note that this happens regularily after 4 hours. This happens on multiple systems, but it is disjunct to the previously mentioned error.