If you use Syncthing-Fork on Android, and encounter the error where the app gets stuck on “Syncthing is starting” after starting the service, if you use AFWall+ or some other firewall solution that can block LAN access in apps, try disabling the firewall, or the control of LAN access in the firewall, or specifically “LAN control” in AFWall+.
“LAN control” is bugged currently in AFWall+, and blocks access to Localhost, even if blocking for the Syncthing app is disabled.
There are reports of users encountering this error in the Syncthing-Fork Android app: (Issue #189) It also affects people using the base Syncthing binary on Android (through Termux or something.)
I also encountered the error, and disabling AFWall+, or disabling “LAN control” in AFWall+ helped. In the Github issue above, OP used a rooted LineageOS phone, and AFWall+ is popular on rooted phones, so he might have the same issue. I don’t have a Github account, so I can’t post, but if you have a Github account, and think it might help the users or the developers, you can post this there.
I’m posting here, because it might help people using Syncthing on Android. This also affects people who use the official Syncthing binary on Android, not only Syncthing-Fork. I haven’t seen any other topics for this issue on the forums.