Remote access works for 5 seconds, then stops

Had a power outage, and got a new external IP. No biggie, fixed the firewall (MikroTik) and changed the NAT on the new external IP and the firewall entries.
The Plex server shows the new IP without any problems.
But I simply cannot get i online anymore. I have restarted my Windows 11 with the server on it, and disabled all 3 firewalls, but it only shows online for 3-5 seconds, then it goes offline.
I can see packets going through on the firewall.
I have tried changing ports, but nothings works - how can i troubleshoot?
All the support articles just tells the same, and I have no clue why it suddenly stops.

Server Version#: 1.42.2.10156

Edit: All local playback works perfectly, also on my Apple TV
Edit2: It would help if the media server logged anything when trying to connect, it doesn’t.
Edit3: I just turned everything off in the firewall, and it still shows green for some seconds, so that’s a coding error, not a real status.
Edit4: When packet tracing, I see 60 TCP packages, over 20 seconds, going to and from the server on port 32400, all with a size of 66 and 70 bytes. This happens when I press “retry”. So they must be communicating.
Edit5: Firewall reports the NAT:
dstnat: in:Bridge1 out:(unknown 0), connection-state:new src-mac 00:xx:xx:xx:xx:xx, proto TCP (SYN), 192.168.x.xxx:59547->xx.xxx.xxx.xxx:32400, len 52

Remote access is never working. Plex “optimistically” shows “fully available” while trying to activate remote access. When that fails, it returns to “not available.”

Contact your ISP. Ask if they use CG-NAT addressing.

If yes, ask if they can provide you a public, IPv4 address that supports port forwarding.

Also, see The Basics of Remote Access Troubleshooting.