To close this, as OP hasn’t responded further.
Problem occured when very large number of DaTube and Compressors were in use. Work around solution was to remove 20-30 instances from frozen tracks and, after saving active plugs settings, replacing original plugs that were affected and loading up saved settings.
Not a perfect solution as I couldn’t see why multiple instances of plugs would make this problem appear in the first place (it did transfer to my system, so not a local issue). Anyway, I guess OP has moved on and perhaps contacted Steinberg for their comments.
P.