Just passing along in case anyone else comes across this. I'd sometimes get in a state with a project where I would click and grab an insert effect and want to move it to a different slot on the same track or another track. I could click and drag it, but letting up on the mouse button would not release it. This issue persisted until I actually rebooted my Mac.... quitting and relaunching DP didn't help.
It ended up that the culprit was USB Overdrive. I removed it and I paid the fee for the latest version of Steermouse, and no problems.
Passing this along in case it helps somebody.
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