To be more precise; if all points are selected and specified as "sharp" and then you select any one point to move/drag the point - the "sharp" points next to it - on either side. are changed to "smooth" points - undoing all you were trying to do with "sharp" points.
Trying to reduce this to a very simple example (simple rectangle, mine was more complex) The problem may be related to the fact that clicking on a simple rectangle "sharp" point converts it to a smooth point - clicking again makes it sharp.
There should be a way to make anchor points "stick" to the type of points specified.
Pixelmator Pro Version 3.6.4 (Archipelago)
Apple M1 Max, 32 GB, Sonoma 14.5