Hello Patrick, thank you for your reply.
I have been using Affinity Publisher Beta 188.8.131.520 (although I see a new beta is now available). I am using it on a Windows 10 PC with a AMD Ryzen 7 2700 processor and a Nvidea 1060 graphics card. I publish a regular 12 page newsletter which I forward to a colleague who uses a MAC. My original was perfectly formatted when I sent it, but when he opened the file on his MAC there were many text boxes with overflows. He corrected these and sent the file back, but when I opened it on my PC, I had the same problem with text overflows.
The file sizes are about 13 MB so too big to upload here. I could send them via a dropbox link if that would help. Here is a screen grab showing one page from my colleagues MAC version and showing text overflow