Hi,
I suddenly was unable to connect to my VPNs while avast firewall was on.
I found that in "packet rules" of firewall there where rules blocking ports 500, 1701 and 4500
To be able again to connect to my VPN (as I was used until a few days ago) I disabled the above rules.
I presume the above rules where inserted from an Avast update but I'm not sure.