Thanks, but nope there were not two instances running.
I just ran another test – rebooted the PC, restarted both phones, opened the B4A file and then alternated bridge connections between my two phones, the G3 and G4.
When compiling, downloading, running under debug to my G3 I got debug log statements. Without closing B4A when compiling, downloading, running under debug to my G4 I got no debug log statements. I did this back and forth several times with the same results.
I am using a Windows 10 computer to run B4A version 7.30.
I am using a Windows 7 computer to run B4A version 4.30.
Tomorrow I will try loading B4A version 4.30 on my Windows 10 computer to see if debug logging works with both the G3 and G4 as it did with Windows 7.
Searching with Google I found G4 posts concerning MTP and PTP USB modes when using USB debugging. There also was some mention of Enable OEM Unlock in Developer Options. These suggestions did not seem to apply.
Barry.