Welcome to the board, Beermusic!
I am not exactly a MAC expert (i never touched one

), but I can tell that even for PC users some have issues depending on their boot order.
Anyway, I would always recommend to boot up your Tascam last in line. Why? Modern CPUs are ever so fast, sometimes a process for USB-ports is skipped. If your system is running, usually all the important drivers are loaded - if you now connect a device or boot a device per USB chances are, that a mount process is re-initiated and everythin will run fine. At least, this always worked for me:
- PC (until my desktop appears)
- Tascam
Despite this, other people had other results with other booting orders. It depends greatly on your system, ports, mainboard...
Interestingly
if I power down the Tascam after session and close Logic, but without shutting down the Mac, the next time I boot up the mixer it doesn’t interface correctly if I reopen Logic
this is contrary to my advice. You see, there are some grave differences.
Is Logic the only app using contact with the DM?
Some years back, I had a similar problem with Samplitude. Samplitude wouldn't find my DM, but Reason 8 did. Since Win10 I did not encounter any problems of this kind anymore - but since you're on Mac, that's a different story.