subform table not printing correctly as .pdf

I have an existing database with a number of forms - I run Ubuntu and following an upgrade my Libre Office was uprated to 5.1.4.2. Most of my forms are fine and print correctly but a form I use which has a subform table with multiple records has a peculiar corruption when I print it as a .pdf.
The column header text disappears and I get text in the background of the column header which I cannot read as the text is larger than the header row so only partially displayed.
i thought that my form had corrupted but had the identical problem with a new one I created and the same with a subform table I created within a report as a test. I can’t work out why this is happening and my other forms are printing fine – it’s only the form with the subform table which has problems.
Is there any solution to this as I use base every day and this particular form is an invoice so it’s fairly crucial that I can print it as a .pdf Any help much appreciated

I have not managed to resolve this but have now discovered that in print preview I am getting the same strange subform table header problem. In print preview I can clearly see the text is my the column header text but in an overly large font - I cannot see a solution to this as there seems to be no way to change the size of the font in the column header.