Sheet looses formatting after or during shutdown

I have a number of Balanced Scorcards that I distribute to a wide user base. These scorecards are macro enabled workbooks with VBA code controling things like user functions and product authentication/licensing routines.

The following problem has begun to drive me crazy. It started only very seldom but is increasing in frequency. I cannot reproduce the probelm. The latest example of this happened on a machine with the following specs:

Windows 8.1

Office 2016

i7 processor

8 Gb memory

A fairly strong machine which rules out 'resource' issues. My onw machine is an i3 with 4 Gb memory running Office 2016 on Windows 10.

This happens during shutdown as the problem only reveals itself after the workbook has been opened again.

Certain sheets (there is no pattern as to which) are ending up in the following state:

1. All protection removed - the sheet password is removed and the sheet left unprotected

2. Column and row formatting is removed

3. Hidden rows and columns are unhidden

4. Sheet VBA removed - sheet bound VBA code is removed

5. Frozen rows left unfrozen

6. All data validation (drop-down lists) removed

7. All merged cells unmerged

8. Grid is shown - normally hidden

The following images show what the sheet should look like and what it ends up looking like:

Before:

After:

Can anyone tell me what is causing this and how can I prevent it from happening.