Sounds more like a TLS/security problem when the system starts and you can´t access the web interface.
When you have updated to a later 5.6, 6.0 or 6.1 the system uses in most countries TLS on port 443,
so try to deactivate TLS on the phone and set the port to 80.
After that restart the MFIM and try to access it again via http.