@donho
Sometimes there are users (like me) that do some silly thing, that are not expected.
In version 8.6 a new style had been introduced: “Multi selected text colour”. The effect for me was, that in column-select mode the selection was shown only partially (last line only). It took me some time to find out what was my fault. I use a personalised style, where the default background colour happens to have the value “C0C0C0”, the same value as the background for this new style. Therefore I could not see the selection because it had the same bg-colour as the rest of my text. For “Selected text colour” I use the value “A0A0A0”; after applying this value to the new style, it worked again.
I know, it is really a very special case, but it may happen. A similar situation might arise with other changes in the future. For these cases it would help to have a backup for comparison.