We made sure to include the right version of Jack backend, built it from source ourselves, it works. 
patch@patchbox:~ $ jackd --version
jackdmp version 1.9.12 tmpdir /dev/shm protocol 8
What are the steps you’re taking exactly? I just flashed an sd card using [Beta] Patchbox OS image 2020-11-23, went with the setup wizard, selected ‘desktop autologin’ so the GUI is up automatically, rebooted, started Pure Data using the shortcut on the desktop, or just running ‘pd’ or ‘puredata’, it runs just fine.