The page text boundary indicators have disappeared in Writer

[PaddyLandau]

LibreOffice Writer displays the text boundaries on its pages, shown by small L-shapes at the four corners.

Having upgraded to version 5.3.0.3 recently, those boundaries have disappeared.

I have checked that View > Text Boundaries is ticked.

How can I get those text boundaries back again, please?

EDIT

I have noticed that this is happening only on some of my documents, not all of them. That means that it is document-specific. This confuses me greatly!

[FlavioMaia]

I have a same problem. My LO is 6.0.4.2 on Ubuntu 16.04.

[FlavioMaia]

I disabled hardware acceleration and restart Writer. Did it and it’s showed the corners marks again!