For me it works again:
Browser:
cleared cache several times (ok, I use private browsing of FF so I closed and reopened) and logged in several times. At one point it works again.
Win10 App:
Cleared chache, not working, deleted folder C:\Users\name\AppData\Local\Plarium\PlariumPlay\Cache\Cache and it worked again.
Probably different servers have different certificate expiration dates.
Be prepared for another certificate expiration on May 1, 2020:
Subject Name
Common Name: *.plarium.com
Issuer Name
Common Name: COMODO RSA Domain Validation Secure Server CA
Validity:
Not Before: 3/10/2017, 7:00:00 PM (Eastern Daylight Time)
Not After: 5/1/2020, 7:59:59 PM (Eastern Daylight Time)
Fingeprints:
SHA-256: 5A:D0:4B:39:71:97:B0:85:D9:90:AB:AE:C5:0C:61:90:58:5D:A5:CA:AC:CA:7D:79:E6:D5:4C:04:9E:BC:6F:F4
SHA-1: 9B:B9:08:CD:9F:15:1A:3C:B6:21:55:0D:F0:A5:26:94:23:67:39:B2