On our Surface Pro 7's we have finally found what was (one of many factors) causing the random shutdowns.
We run Trend Micro "Worry Free Business Edition" (haha) ... Turns out, running Windows 10 build 2004 with Trend causes the random shutdowns when sleeping. remove Trend, SP7 is perfect.
Has been given back to Trend to sort out but for the time being, we are no longer using Trend.