Mouse Cell Selection goes nuts in Large Files

[TRE22]

I have a large *.xlsx file (aapproximately 25 sheets, 7 MB file size)

1) Very Frequently, when I try to select a single cell, with a single left mouse click, multiple cells (15-30) are instantly selected and highlighted. It won't let me select a single cell when this happens (more often than not).

2) Can't select a single row with a mouse click. In this case it starts automatically scrolling up selecting additional rows until the left mouse button is released. I cant click and release quickly enough to select any less than 3 rows.

I went through all the setup options that looked applicable, and did not find a solution.

Any ideas on how to fix this, or is it a program bug? Does the full Softmaker Office also have this issue?

Thanks in advance!