Had to update our SSL certificate from Thawte, got a new one from them and
everything is fine for the devices and they verify properly but I can't get
the web admin interface working, it comes up and tells me there is a problem
with the certificate.

Any idea of what to check?

Only difference is that the public key part from Thawte is 2048 and the old
one was 1024, the problem seems to be in the chain.