I'm not sure if it is the same issue, but I also had problems trying to connect to PPBA due to port conflicts.
First be sure the port you set on INDI is where your PPBA is.
Canonical way of doing things is to map your seria device using
Serial Port Assistant
.
For me this didnt work.
When this fails because another device gets the port first, you can manually add to the created rule file the serial ids in order to differentiate between devices.
as explained here
In my case, found that in /dev/serial/by-id there was a symlink pointing to ../../ttyUSB1.
The file was named usb-Pegasus_Astro_PPBADV_revA_PPBA4PSFVS-if00-port0
I used this symlink name in the INDI communication port for PPBA: /dev/serial/by-id/usb-Pegasus_Astro_PPBADV_revA_PPBA4PSFVS-if00-port0