Check whether the docker service for LN Market is starting properly at all, logging into your node via terminal / SSH / putty
ssh -t umbrel@umbrel.local
docker ps
ghcr.io/ln-markets/umbrel:v1.1.5 "docker-entrypoint.s…" 8 days ago Up 8 days (healthy) 0.0.0.0:4242->4242/tcp, :::4242->4242/tcp lnmarkets_lnmarkets_
Use your umbrel user password for login. Look for the line of LN Markets. Is it restarting?
You may try to de-install and re-install and check docker ps again whether it solved it. If not, report back here with your debug log (in the UI > Settings > Troubleshooting Logs)
What is the URL you are accessing from? I am able to access lnmarkets through TOR, but not through local IP (192.168…), I get a blank page also when I do