Google search for this sort of report found several, but not many with solutions that worked.
Volume auto-dismounts at seemingly random times was one of them, and I notice that it’s in VeraCrypt’s forum where you might be able to find others, or if not, maybe report symptoms.
--concurrency-block-hashers (Integer): Specify the number of concurrent
hashing processes
Use this option to set the number of processes that perform hashing of
data.
* default value: 2
Reducing to 1 might be able to make the drive slightly less busy, but it’s doing other things too.
Channel Pipeline describes, but even GUI will show it’s counting files while also reading files…
--use-background-io-priority = false
to use the lowest IO priority level, which can make operations run slower
might slow it by yielding to other I/O, but is there any other I/O active that would make it do so?
If you have or can acquire other USB devices, you could see whether this seems like the cause.