Expanding a set of grouped rows causing excel to freeze/crash

I had the identical issue this week on Excel 2019 on Windows 10 (Interestingly: the identical spreadsheet does not experience the problem on my iMac running Excel 2019 on Catalina). After 30 minutes I was close to replicating & eliminating the problem at will on Windows.   It was easier to eliminate the issue than triggering the issue to re-occur. The symptom "appears" to be a freezing excel app, but that is not what's actually happening. It's more of a visual zombie issue.... What's actually happening is that the Excel app is still running but it's "window painter" stopped updating the Excel window you are seeing; but the commands you are typing are still being registered by Excel. This notion is proved by several ways: you can expand the excel window and it will not repaint any of the expanded area, the task manager shows it's running (i.e., it's still responsive), you can update data within a cell, you can switch tabs, etc.  Then if you "save the zombie excel file" all these changes will be in the excel file once reopened; hence, be careful not to accidentally change data while in the visual zombie state. To eliminate the "visual zombie" issue, what I've found to work was: 1) open the spreadsheet but don't expand the grouped rows yet, 2) ZOOM out until all rows and columns are visible within the viewable window (to be extra safe, I had extra blank columns and rows to the right and below the data area); 3) Once fully viewable, now expand the grouped rows that would overlap the horizontal freeze line; and it should work find and the visual zombie should be gone for good.  4) Save the spreadsheet.

So, it appears having the entire data area viewable at the start (i.e., before expanding) allows EXCEL to learn the proper row expansion ruleset without corrupting its window painter; and once save the spreadsheet will behave thereafter, including zooming in/out to your proper viewing scale and saving at that zoom scale.  Once eliminated, I haven't figured out the exact triggering sequence [but I triggered it nearly a dozen different times with test spreadsheets], but the problem manifests itself only when a combination of several excel elements are involved: A) Horizontal Pane freeze is ON; B) Row grouping is ON; C) the expansion of the grouped rows MUST overlap the horizontal freeze line once the group is expanded; D) and [potentially] AutoFilter is ON the rows that get "overlapped"; E); Column Groupings are enabled; and F) All the columns are not within the viewable Excel window.   Play with this and you'll surely stumble into the visual zombie. Hope this helps