Stange https webserver certificate error Catalina 10.15.4 + Firefox/Safari

[Schroinx]

I have troubles reaching some websites, as both Firefox and Safari report them as having invalid certificates. I have checked with the webmasters and they report the certificate is valid and no other users are reporting any problems. There are some add-ons in ff that could cause such behaviour, but they should not be a problem in Safari...
The time on my macbook air is updated automatically and reporting the right time and time zone.

I am at a bit of a loss here as to why this happens.

 

[Schroinx]

I tried with different browsers and user accounts and to clear the cache in the OS all to no avail. Then finally I tried opening the problem webpage from my phone over the local wifi, and it was still an issue there, so I reset the router and it solved the problem.