"error: JACK error: cannot lock down memory for RT thread (Cannot allocate memory)"
this error seems to indicate that you are lacking real time priviliges (what's the content of your /etc/security/limits.d/audio.conf?)
I can reply later, I can't access the computer where this happened.
This one appears when I load a complex patch. It also crashes Pd:
"tk scaling is 1.3187954309449634 Speicherzugriffsfehler pd_gui: pd process exited"
you could try to produce a backtrace [1]
Funnily, Pd+Jack works with the same patch - as long as I start Pd with alsa, and after loading the patch change the audio to jack.
which would indicate that your patch takes too long to load and jack kicks out Pd....
the patch does need some time to load, it has to load in a couple of long
samples (up to 5'), load text files with markers that divide the arrays
and generate data structures to display that division... can take some
minutes in XP (will take less on ubuntu, of course).