Just posting for anyone else who might run into this problem.
I upgraded to 26.1.4 and all my permitted networks lost Internet access. I saw some access being blocked on Firewall (hitting default Deny) even though my Firewall rules were correct and had not changed during the upgrade.
I solved my particular issue by removing my WAN Gateway and then re-creating it with the same settings. Figured worth a post just in case anyone else gets the same issue.