[6.4.3] Problem with Microsoft servers

We've been experiencing problems with Microsoft servers (Windows Update, Office365). Windows Update: client (Windows 10) says it cannot connect to Windows update servers. Office365: client (Windows 10) says it has no internet connection. We also had problem with certain HTTPS website but it was solved by upgrading from 6.4.2 to 6.4.3.

I've done various tests and it seems that it does not work if: 1) proxy mode is enabled 2) AND any other security profile is enabled (except SSL inspection). But it does work if: 1) proxy mode is enabled AND any other security profile is disabled except SSL inspection 2) OR flow mode is enabled and any other security profile is enabled.

Debugging has not revealed a thing so far.