QObject thread warning when loading a controller mapping (virtual VirMIDI 2-0)

[ronso0]

Bug Description

warning [Controller]  ------------------> PM: num_sam changed: 64
warning [Controller]  ------------------> PM: add sam 4 "[Sampler5]"
warning [Controller] QObject: Cannot create children for a parent that is in a different thread.
(Parent is PlayerManager(0x55f496df4e90), parent's thread is QThread(0x55f48d560ed0), current thread is QThread(0x55f49976f310)

noticed when tracing sampler creation, see #12809 (comment)

I also get many leaked controls. I assume these are sampler controls, but I can't be sure because only the first control is logged, the I hit a debug assertion
DEBUG ASSERT: "success" in function virtual ControlObject::~ControlObject() at ./src/control/controlobject.cpp:45
Not sure what's happing there.

Mixxx 2.4-beta with vurtual device from snd_virmidi