I have my problem with OWC TB3 dock and Dell P2715Q. I will try an older dock that I have in the office (Kanex TB2 Express; as the name says, it is TB2, thus extra dongle needed); but playing around with different TB docks can get expensive...
I use a Dell XPS 13 with 3 external monitors via a Dell TB16 dock (which uses external power). I wonder if that setting solves these M1 issues (via the extra power) or not. I understand CalDigit docks also have external power but don't know if there can be a subtle difference.
The OWC TB3 dock I'm using is also powered externally. Docks by CalDigit are different docks than OWC, but I think they are all using the same chipset underneath.
It also does not happen with Intel Macs, which use Intel TB implementation. With M1, the TB is brand new, so some issues are to be expected. I suspect that with sleep and wakeup, there is some state mixup with previous link training, so it doesn't talk to other side the way the other side expects. This might be - or might be not - fixed with firmware updates.
I have my problem with OWC TB3 dock and Dell P2715Q. I will try an older dock that I have in the office (Kanex TB2 Express; as the name says, it is TB2, thus extra dongle needed); but playing around with different TB docks can get expensive...