Here’s a Publisher document with three sidenotes near the bottom of a text frame. The first note is a rather long one.
Notes 2 and 3 aren’t visible. Not on the page where the note references are, not on the next one.
When the third note moves to the next text frame (e.g. when inserting text before the first note), notes 2 and 3 both appear at the top of that page.
I suspect the reports of Publisher crashing when converting footnotes to sidenotes are related to this. In a document with longer footnotes these notes were converted to endnotes without problem, trying to convert them to sidenotes resulted in Publisher crashing.
Publisher 2.0.3 / MacOS 12.6.2
TestSidenotes.afpub