Because many times I experience delays, the java process sometimes hogs the CPU.
Still haven’t seen this on OH3 though.
On my Ubuntu server 18.04LTS sometime a process called agetty also hogs the CPU.
That said, in my case the transfer from 2.5.11 to 3.0.0-1 has been silk smooth for Z-Wave.
Aeotec gen5 stick. So there is hope.
I would suggest setting the zwave binding to TRACE logging and also look for hints in the events log.
Another thing you could try is putting the zstick on a powered USB HUB, just for testing.
I run a pi4 system at my summer house, and had to do that with a Conbee Zigbee stick. Seems the pi4 is noisy if you have it too close. Could apply to Z-Wave as well. Worth a try …