The common name (CN) on the certificate is blank which is frankly very weird. SSLlabs gives it a pass but you can see from the report that the common name is blank. It would not be surprising if this resulted in some problems here and there.

Update: in Corion's post the openssl trace inlcudes this:

Certificate chain
 0 s:
   i:C = GB, ST = Greater Manchester, L = Salford, O = Sectigo Limited
+, CN = Sectigo RSA Domain Validation Secure Server CA
[download]

which explicitly confirms that the Subject (the line containing "s:") of the server certificate is entirely blank.