I cannot reproduce this issue in a new document, I'm attaching a file where the bug is present.
I have an object pinned in a text frame. Pin's type is set to float.
The issue occurs when I'm resizing text frame. My object gets scaled. Moreover, undoing text frame resize doesn't fix object – it remains scaled, I cannot undo it. I'm getting the same behaviour with inline pinning (scale to: no scale). I'm attaching screenshots – first one shows original view, the second one shows view after text frame transform and a bug visible on red rectangle.
If there is any workaround to fix this behaviour I will be grateful, because I've got a project with hundreds of pages, lots of pins and I need to resize text frames to put in illustrations and... yeah
My specs:
MacOS Catalina v10.15.5
Affinity Publisher 1.8.3
broken-document.afpub