Same problem for me trying to install the License from the player ( "Cannot contacting the license server") on Linux Mint 19.3. Tried from the shell with mediacenter26 /RestoreFromFile <mediacenter 26 master file.mjr> and I get this new/different error
"error: expired license file or time/date error
CRegistrationHelper::RestoreFromFile: bInstalledOk is false, error = Unknown Error"
I have paid for all licenses for years and I think it was last year, or maybe 2018, I have been buying/using master licenses without problems until this latest release? Date/time is also correct. The same licence works fine on my Windows machines or the media server (Windows 10) it runs on. I even tried renaming the mjr file without spaces (license.mjr) and got the same error. Strange
Any ideas?
UPDATE:
PEBKAC error (user). I did not realise the .mjr files are time-limited and had used on old one. Did a restore for a current mjr file and it worked fine from the shell. Just not from the software itself under licensing.

All good now.
Just bought the Android app so looking forward to trying it out