I had my pi running on an older version of OSMC, from a few months back. It was freezing so I did a new download and fresh install.
I haven’t changed any of the Avahi settings or anything so I have no idea why it isn’t working. Last time it worked out of the box if I remember correctly.
I was waiting for you to provide the appropriate logs to investigate this further; however I suspect this is a local / network issue as there do not seem to be any other reports.
Hm, I don’t know what the issue is (the logs do not load); however I’d say that if you have introduced a new router, that may well be causing the issues.
If you have an opportunity to swap back to the old one to test, it would be worth doing so to see if the problem lies with the router and if there is a configuration option you can change.