Affinity Publisher Version
Latest, I've just bought and downloaded it from App Store.
macOS Catalina, 10.15.3
MacBook Pro (15-inch, 2018)
2.2 GHz 6-Core Intel Core i7
16 GB 2400 MHz DDR4
Radeon Pro 555X 4 GB
Intel UHD Graphics 630 1536 MB
Steps to reproduce
I couldn't reproduce the error in a new document, but I have attached the document where the crash occurs along with a screen recording.
Add Frame Text with Frame Text Tool
Change it to vertically justified
Add picture frame with square text wrap
Try to resize frame text