I wouldn't expect the transmit to timeout, but the Ping-Pong app is a somewhat quixotic/metastable application that can't decide what mode it should be in.
I would recommend making two forks of the app, where one is committed to being the transmitters, and the other the receiver.
In the earlier versions of the LRWAN libraries these things worked out of the box, and would connect at some point if left alone, or restarted at different phases.
Radio is hard to debug, even harder remotely. You're going to have to work though these things methodically, and understand what the code is supposed to be doing vs what is happening.
Make sure both use the same frequency and radio settings. Make sure to use the frequency band allowed in your jurisdiction.
Make sure you have the antennas on, and they are not against metal surfaces.
