Reproducible on Mac OS 10.15.7 and Windows 11 with affinity publisher 1.10.5 HW acceleration has no influence on the behavior.
When I group elements which have a frame or shadow and apply a constraint on one of the elements shadows and frames which lays outside of the outline of the group, disappears. As I understand it, this should not happen.
To reproduce, group two elements where at least one has a shadow or frame and then set a constraint on one of them.
Or take the attached test file ShadowBug.afpub
Select one of the text elements.
Now select any constraints and the shadow gets cut.
Thank you for investigating the bug.
ShadowBug.afpub