Yes, I was very happy with the technician, Marwan (hope I'm spelling his name correctly), that visited me.
He did call me back the next day as promised and gave rather detailed/informative feedback. They checked and it seems the signal strengths and all are good outside the apartment and inside the building. According to him, it means that the problem could be somewhere within the flat.
It's been 2.5 days since he's installed that return path filter (thanks for telling me that's what it's called 🙂 ), I have restarted the modem at that point and the Post RL errors have dropped significantly since then. So it seemed to have helped.
Thanks for sharing that article, will read it shortly. I have to add that my TV is a 2021 high-end model - just noting this as reference to the title of the article 'The old television that brought down the village's broadband'. Will read through the article soon...
After 2.5 days of uptime since the return path filter has been installed, as you can see in the attached Word file, there still is some Post RL errors. I'm not sure if this is a negligible amount or is this still worth looking into? Also, I see some T3 upstream timeouts.
@Paul @Jacob Thank you all in advance for your thoughts/feedback on these results!