I have been on Talktalk phone support and chat to resolve this but nobody seems to know what to do. Everyone in the household is unable to send or receive messages through whatsapp when connected through wifi. No problems on identified when using other networks.
The issue was resolved briefly when asked to switch off scam protection but quickly returned.
I have changed the DNS as instructed and all seems ok.
As you mentioned, this is bypassing all homesafe settings of which I not happy because I have kids in the house who needs some kind of protection.
I hope this gets sorted pretty quickly otherwise i will be looking elsewhere.