The cert of nap.bg and the recent bulgarian tax SNAFU

[Georgi Guninski]

Since 2019-07-15 there is a major SNAFU in the BG
tax authorities. World and dog tax information and ID
leaked on the interwebz.

I have sporadic SSL failures connecting to https://nap.bg
with firefox, lynx and openssl s_client.
e.g:
$ openssl s_client -connect nap.bg:443
Verify return code: 21 (unable to verify the first certificate)

On the other hand, ssllabs.com claims the Cert is OK, grade B.

Is the cert of nap.bg OK?