For about 1-3 months now, I've been unable to connect to either Radarr or Sonarr.

I've verified the correct API, correct internal IP, and port are correct. I've also forwarded the ports in my router.

I've tried emailing support, back in Sept, received no response. Read through the threads here on the forum, none seem to be a closed loop; most seem to end with more questions or confirmation of continuing issues like mine.

If anyone is able/willing to assist with this, I would greatly appreciate it.
Versions of Radarr and Sonarr? Since it is both applications, unlikely to be those.

1. Connection within the LAN all good, so all services run correctly internally.?

2. You are running a simple port forwarding on your router, and there is nothing of note going on there?

3. I appreciate that it is difficult to remember, but no changes on the network since the change. The router isn't new. IP address you are forwarding to internally is static? You control the updates for your router, nothing the router supplier could have updated via auto update?

4. Are you using port forwarding for any other services, or something that you can use to test that an alternate service works.