Pianoteq 8 LV2 plugin on Linux - feedback loop in Ardour/Qtractor

Hi all,

I couldn't find anything in the forum already, but has anyone tried the Pianoteq 8 LV2 plugin on Linux yet? I tried using it in Ardour 7.1.0 and Qtractor 9.27 and when playing any notes from within the UI or via MIDI input through the respective DAWs, I get enormous feedback (like PTQ is in a feedback loop with itself), and lots of XRUNs from JACK along with 100% CPU usage on a single thread. The standalone client works perfectly with the JACK backend, and the LV2 plugin also works perfectly in Carla. So it's something that Ardour and Qtractor are doing with the plugin which Carla and the standalone plugin are not doing. Pianoteq 7 LV2 doesn't have the same issue and is working perfectly on the same setup.

Pianoteq 8 standalone: Works normally (tried with JACK only)

Pianoteq 8 LV2:
Carla 2.5.2: Works normally (tried with JACK only)
Ardour 7.1.0: Feedback loop + 100% DSP load + XRUNs (tried JACK and PulseAudio backends, same result)
Qtractor 9.27: Feedback loop + 100% DSP load + XRUNs (JACK only)

Setup: AMD Ryzen 5900X 12c/24t running Ubuntu 22.04 LTS, GNOME desktop, KXStudio repository. JACK + PulseAudio for sound.

Screenshot here showing Ardour, Ptq8 and spectrum analyser of the feedback: https://imgur.com/a/Yy51XHz

edit: for what it's worth, even with the Ptq plugin audio outputs disconnected in Ardour, it has the same issue.