https://community.talktalk.co.uk/t5/TV/Channel-4On-Demand/td-p/29107@Roy thanks, beat me to it. I posted on their thread on TalkTalk too.
Greetings and welcome to the Community!
The problem you have, though, is because the adverts and the programmes on the commercial channels are provided from different servers.
The handover to the ad server is always handled impeccably (surprise surprise! - but follow the money) while the handback is famously iffy.
Ofcom ought to have a rule to say that if the broadcasters can’t hand you back to your programme after an ad break, then they are not entitled to charge for serving them.
But until that happy day, the best thing you can do is complain to the offending broadcasters.
@lowecheryl2023 recommend you try the method in the link above.