Please post screenshots the GUI’s home page, and also of Actions / Settings / Connections from both of the two non-Relay Devices.
Is there anything in the Log that shows what’s going on? Can you induce the error with the “relay” debugging facility turned on if not? Feel free to post your log, or at least snippets.
relay://bridgemode.bounceme.net:22067/?id=XWPAO25-SAO6M33-5I5WYJH-SMDM4A4-OLOI4B5-E2OC3S2-JZXUSDM-FUZQGQD
or by relay://92.239.74.95:22067/?id=XWPAO25-SAO6M33-5I5WYJH-SMDM4A4-OLOI4B5-E2OC3S2-JZXUSDM-FUZQGQD
When you hover over the not found error, does it say “incorrect response code 1: not found”? That’s what it shows for me.
I think the other device is not connected to the relay.
You might have to add it as one of the Sync Protocol Listen Addresses on the other device (available in the Connections section). For example you can set the listen addresses to default,relay://bridgemode.bounceme.net:22067/?id=XWPAO25-SAO6M33-5I5WYJH-SMDM4A4-OLOI4B5-E2OC3S2-JZXUSDM-FUZQGQD to make the device constantly connect to the relay, but still keep the default listeners.
In Catfriend1’s Syncthing-Fork (or the discontinued official Syncthing Android app) you can set the listening addresses in Hamburger (3 bars) → Settings → Syncthing Options → Sync Protocol Listen Addresses.
As @marbens already said in post Can't connect to my Relay - #5 by marbens, it appears that both devices are dialing in Temporary protocol submode. This can’t work, as at least one side must have “joined” the relay first, by opening a permanent session to the relay. The linked post explains how to configure this.
One at least one (ideally both) devices, open the Sync Protocol Listen Addresses (Actions → Settings → Connections) and set the listen address as prescribed above.