I hope this might help someone and maybe someone out there can explain why this seems to work.
I had followed the guid for persistent port mapping as described in
I have an EQMod mount and couple of Pegasus devices and a Senso Sesto focusser.
This all worked fine for many months until one evening I had to re-boot the Pi (running on a Pi4). After the reboot I could not get my Pegasus PPB or Pegasus Focuser to connect.
I double checked everything but I could still not get it work. The EQMod was still working.
I noticed that the entries I had created in the rules file for the Pegasus devices started with SUBSYSTEMS=="usb" but the entry for the EQMod mount started with SUBSYSTEM=="tty" (so now SUBSYSTEM instead of SUBSYSTEMS and tty instead of usb).
I changed the pegasus entries to use SUBSYSTEM=="tty".
Now everything is working fine again. I also added my Senso Sesto focusser using SUBSYSTEM=="tty" and that works too.
Not sure why everything worked in the first instance and then during one evening stopped and I am not really sure why the change I made fixed the problem.
Anyway I am now very happy that all is stable again. Anyone know why?