for ages I've always advised for not doing send/return inserts from and to qtractor itself: it used to work just partially and on very specific situations, while using *genuine jackd1 or jackd2; but on pipewire-jack substitution, things got a lot different and to the worse: while it used to work fine on all scenarios a few releases back (pre-1.0.0 iirc.), it stopped working on-and-off or not at all on newer versions.
so the writing is still on the wall: directly connecting a same jack-client (qtractor) output ports (insert sends or output buses) to its own input ports (insert returns or input buses) is still not advisable.
just a few topics on the subject, even predating the pipewire advent:
not sure whether pipewire also does the so called zero-copy optimization as genuine jackd; you may confirm it, by connecting any other client but qtractor to the designated inputs and check for your self whether the signal starts flowing in...
seeya
for ages I've always advised for not doing send/return inserts from and to qtractor itself: it used to work just partially and on very specific situations, while using *genuine jackd1 or jackd2; but on pipewire-jack substitution, things got a lot different and to the worse: while it used to work fine on all scenarios a few releases back (pre-1.0.0 iirc.), it stopped working on-and-off or not at all on newer versions.
so the writing is still on the wall: directly connecting a same jack-client (qtractor) output ports (insert sends or output buses) to its own input ports (insert returns or input buses) is still not advisable.
just a few topics on the subject, even predating the pipewire advent:
not sure whether pipewire also does the so called zero-copy optimization as genuine jackd; you may confirm it, by connecting any other client but qtractor to the designated inputs and check for your self whether the signal starts flowing in...
seeya