Excel 2019 every so often will not let me select; today it was two adjacent cells, one with text, one with a number. I could click on one but Shift-Arrow would not extend the selection. I was able to get it working again by selecting Sheet 2 (empty) and then back to Sheet 1. Can anyone explain what is going on? Help says that F8 can be used to turn on/off Extend, but I don't use F8. And using F8 turns on a label Extend Selection but it seems to work the same with it or without.
This could be related to another problem, the Enter key often causes a jump to another open spreadsheet. It should be selectable whether to move down or move right, and for now I have it do nothing.