Hi All - this has been a difficult issue to diagnose, and we still haven't found a reliable way to reproduce the problem. However, based on all the evidence, especially from this thread, we've been able to speculate on the cause and we are planning to release
an update with a change that we hope will fix the problem for Excel. The proposed fix should be available in the Insiders Fast release next week (week of 11-May).
We would greatly appreciate if you would update to the Insiders Fast release next week and then report back here about whether the problem goes away or not.
Many Thanks in advance.