I experienced something similar with RD and Kodi last year. I suddenly started getting errors attempting to reach RD on my google TV. Using a VPN, everything worked fine, but without the VPN I'd always get errors. Using a VPN with a debrid service can also be iffy, and I got dinged by RD for the VPN switching IP automatically (despite the VPN I was using supposedly being on their whitelist).

What I determined after some digging and testing was that my ISP started blocking RD traffic in their locked down router settings (one of several ISPs that now do this), and my fix was to finally ditch their garbage router for one that I have control over.

Your situation isn't identical, and I know little about that brand of streaming box, but it could possibly be an update or setting interfering or the manufacturer intentionally trying to prevent users from using their devices to access "pirate" services. Might be worth trying some searches with your model of thomson and your ISP to see if others are having similar problems with that hardware recently.

If you use Torrentio with Stremio, Torrentio blocks VPNs, though I don't know why a VPN block would be impacting one platform but not another.

I use stremio+torrentio and it's recently-ish stopped working when I use (any, as far as I can tell) VPN server :/

Could it be your DNS provider?

Oh, and the VPN is on the approved list.

It can't be the ISP because everything works on my phone and PC.