Sharing something that bit me in the ass and ended up spending good half of afternoon trying to debug.
Was setting up reverse proxy in front of my syncthing instances so I could standardize the security of the devices since some had internal access only vs others which were on a public IP.
All worked except one host would give me a “too many redirects” error.
Took me ages to figure out since everything was fine when directly accessing from behind my firewall on both http/https but everytime accessing via the proxy it wouldn’t.
When really almost ready to give up - I recalled the “use https for gui” setting and checked it out - it must have been set at install for this one host (and no others!) and that was what was causing the issue (since my reverse proxy was doing the TLS termination and passing traffic to syncthing via http)
Is there any reason syncthing won’t look at the X-Forwarded headers before deciding to redirect to https? That would have avoided this hiccup…