Just tried power cycling the computer and devices including turning the modem off and on again, but the persistent brief audio drop outs continue
Not sure I understand the question about how I'm using USB, but the EHD is connected to the Macbook by USB-C with an adaptor for the Mac's USB-A port. The DAC is also connected by USB but without an adaptor (ie it is USB-A). Sorry if I've misunderstood you.
In any case, as I said, MC26 works fine with the same devices