Some borders consistently don't display

My spreadsheet looks like this: 2020-02-02_0946

As you will see between rows 2 & 3 there is a purple border, but not in all cases. However there is one defined. To try to diagnose and resolve this I have

  1. checked both by doing Format Cells, Border on both rows 2&3 together and separately.
  2. completely removed all formatting and then applied afresh to no avail - and the missing bits are almost, but not quite, consistent with the way they were before.
  3. Check print preview - borders ar missing
  4. Printed - borders are missing
  5. Veiwed and opened in gsheet - borders are present

Even stranger is that if I Insert a row above the result is this: 2020-02-02_0949
So you will see that the intermittent display has changed to not show the border in different columns in the new row.

It feels like an ‘old fashioned’ memory problem except that I have plenty and it is alway consistent. Although there are three columns with Index and match formulae in about 350 rows.

Has anyone else experience this, and found a solution?

Did you ever increase the zoom level?

Verify with the option Menu/Tools/LibreOffice cal/View/Visual aids - Grid lines to Show in colored cells.

made no difference