Nuendo 11 crashing with Syncststion

We have just upgraded to N11 and had issues with Syncstation, normally very reliable, and I’m wondering what to do - all advice gratefully received.

During a recording with Nuendo following external TOD timecode via the LTC input of Syncstation, we had 2 crashes at random intervals. Both were where Nuendo stopped syncing to external sync.
App could see LTC coming in and Syncstation appeared to be working normally (thankfully as it was providing sync to the whole shoot!), but N11 suddenly dropped out of record and then wouldn’t play or record while external sync was active. We’re using the new 64 bit driver on Mac 10.14 (Mojave). We have another 2 recordings for this client next week and would really like to at least understand what’s going on. Both crashes were after about 15 mins while recording a 40 track multitrack via RME Madiface XTs.
Was thinking of going back to 10.3, but we couldn’t get it to recognise VST system link for some reason. Think 10.2 may be safest unless anyone else thinks otherwise.

And don’t get me started on Eucon! We have just obtained an Avid S1 and it has amazing potential. Beautiful but crashes constantly, particularly when moving or re-ordering channels.
Was looking enviously at my colleagues Pyramix which worked flawlessly throughout the recording. I was wanting him to switch over, but maybe that will have to wait a bit now!