The Remote has new batteries, and the most recent software (version 1.3). The problem began when I added an engine to button 3. The engine on button 1 has bluetooth app capability (which obviously I'm not using), while the engine on button 2 does not have bluetooth app capability.
The recent addition to button 3 is a baby Lionel GG1 with bluetooth app capability, and although I'm not using the app, in order to get the engine to link to the remote, the Bluetooth switch on the bottom of the engine must be enabled.
I use tubular 031 track with conventional train operation via ZW and KW transformers.