@gwen-dragon
Gah!
It's WIndscribe (VPN Extension) - it has an adblocker enabled by default that I hadn't noticed which interferes with pages even when you're not actually using the VPN agent.
so, problem solved.
Just for interest's sake, --no-sandbox is enabled because otherwise Vivaldi won't run on my Linux (Puppy Linux 'Tahrpup') - Puppy runs as default as root.
[Anyone reading this who wants to lecture me about how "dangerous" it is to run as root, please bear in mind that I've been using *nix systems since 1985, and Puppy since 2006. I also run all my Windows boxes as with administrator privileges. I'm happy to take responsibility for my computers and what I do on them.]