I had the same problem with the MK2 devices when I had their USB cables connected directly to the Mac USB ports while on these betas, including this current one. Three weeks ago I bought the Overhub, and now I’m able to MIDI Sync without dropouts. I can even use all of the different MIDI sync options with the DAW, including SPP and Pattern Mode for 1-16 bars (maybe more) while staying in perfect sync.
I only bought the Overhub because I truly ran out of USB ports on my computer (stupid iLok) and I had already struck-out with several lower-priced powered-USB 3.0 hubs previously purchased from Best Buy. I did not buy Overhub with any expectations to solve my Overbridge and MIDI sync issues, but it actually did. The price was a bit hard to justify because it’s not very sexy, but it is an extremely utilitarian purchase if you have multiple Elektron devices with Overbridge.