Alas, after working OK for a month or so, it is now not displaying a different aircraft. Can't tell if 347ME is showing or not as it's been away at extended maintenance/upgrade. But, over the last week to 10 days, I've noticed 5199B now no longer shows, even if it's in the pattern with me.
The attached file is the ADSB log for one flight (I thought I had the logger enabled for others but it seems to turn itself off) where 5199B was in the pattern with me, but nothing shows on the display. This time my student didn't have a tablet to confirm.
Looks like the file upload won't work - possibly doesn't liek the 25Mb file size. You can get it off Google Drive here - https://drive.google.com/file/d/1f_O_R5NHe9Hwv76cGcFqXUvkmP7w-Iv3/view?usp=sharing