COMODO RSA Organization Validation Secure Server CA 10 4C 63 D2 54 6B 80 21 DD 10 5E 9F BA 5A 8D 78 16 9F 6B 32
service.oneaccount.com are correct 82 47 E9 19 2A 1C F0 1E E4 BC 51 80 9B 21 46 87 B5 DA 65 D1
are correct, as far as I can see. Further more the root certificate COMODO RSA Certification Authority is from your operating system's Trust Store and, as the name implies, is implicitly trusted. So for the moment I am stumped as to why it should intermittently not be trusted and only when using your Virgin Media connection when all would reference the same Trust Store certificate. Firefox has it own Trust Store and the same observations apply there too.
Out of curiosity are you using Rapport in Safari and Firefox?
Thank you for posting the images. Will work my way through them but I noticed use of depreciated MD5 fingerprint, are you using an older version of MacOS and/or Safari?
MacOS version is 10.11.6 (El Capitan). I guess these days that counts as "older" 😊
Safari version is 11.1.2.
I normally use Firefox for my all my browsing. It is regularly updated.
If Firefox encounters a problem displaying some webpage, often comparing the behaviour of Firefox with that of Safari can help diagnose the problem. I don't use Safari for regular browsing.
On this occasion I used Safari to display the certificates because it actually provides the certificate information when the connection fails. By contrast, Firefox just says The page isn't directing properly and doesn't give any indication that it is a certificate problem.