I actually started a thread about a similar (possibly identical) issue.
It’s been happening to me since at least the first N10 update, on different Macs (MB Pro, iMac, 12-core desktop) and OSs (High Sierra through Mojave).
I’ve been able to identify it as, at least in MY case, length of time the project’s been open. If I’ve been working for more than, say, 4 or 5 hours without a break, it’s time to close Nuendo and open again. Restart not required. But if I don’t… things can happen. Usually there’s a warning sign-- a short, but long enough to notice hang with beach ball. To me that says, “Save now and restart, Dummy, or you know what’s next.”
If I don’t… a serious hang/freeze will ensue sometime in the next 15 minutes. If a file is playing when it happens, audio will continue, but meters will freeze, all system commands unresponsive. If I walk away and let it work it out on its own, two out of three times Nuendo will come back within the next five to ten minutes. If I pound keys and move cursors and try to shift focus to the Finder, it’ll almost always crash the app after that five or ten (anecdotal on this; no hard data).
It happens if I’m using only Nuendo plugins, it happens when I’m using 3rd-party plugins. It happens using my RME FireFace 800, it happens with my Steinberg UR-22.
I’ve learned to work with this, and now restart Nuendo periodically if I’m in a marathon, so I have no crash logs to send. My point here is that it’s clearly an issue (even if the issue is that I’m practicing poor production hygiene by working that long without a break, or without giving the app a break).
I should add, and I haven’t had a chance to test this out yet-- there is the hypothetical, but very real possibility that my issues come from using templates from previous Nuendo versions. I intent to rebuild mine in the name of potentially taking care of it, but have been too busy. Are you using previous version files as templates? That’s been a historical problem. In my case, because I’m working around the issue and it’s not that much of a problem for me at present, I’m waiting for N11 before I rebuild my templates. It’ll take a while.