[davewalker]

I think I may have tracked down what's happening

1. Chromebook going to sleep
With recent updates, this doesn't happen anymore. In other settings I had the 'keep screen on' set to always, but this appears to have been reset with updates. Currently set as 'While Viewing Scores' and seems to be OK.

2. Mobilesheets exiting
This is linked with updates.  If an update from Google Play is pending or in progress, Mobile Sheets will exit while the update happens.  I now check for updates the night before playing and make sure no updates are due and all has been stable since.

thanks

[Geoff Bacon]

You could just disable automatic update for Mobile Sheets and perform them manually when it suits;  you've no idea when the update might become available and one could still get in between your check and the performance (unlikely but possible)

Geoff