Avast Win 10 Firewall makes RealVNC SUPERSLOW...

When I have my avast firewall turned on (Avast internet security installed) 11.2.2262 on my Win10 home and use Real VPN everything is VERY SLOW and LAGS a lot.
This is a deal breaker for me as I need Real VNC to admin my PC from my macbook pro.
I have put the ports and application rules as they should be (allowing traffic on relevant port)… but it does not seem to matter. If I turn off avast firewall everything is superfast. On = superslow.
One note. If I do turn of the firewall, then it seems to be ok speed for a while, then slows down, then turn the firewall off, great speed again…

HELP PLEASE.

So since no-one seems to have a solution, and avast experts (from the company) are not responding I have uninstalled internet security, kept only the free virus scanner, and use Win firewall. Now it works fine.

Contact support: https://support.avast.com/support/tickets/new