Live -- piece disappears from one player's view

No, this problem appears to have originated with the fix described in this post.

https://forum.vassalengine.org/t/bug-in-stackmetrics-merge/2026/1

I have tested by reverting the code on line 665 of StackMetrics.java from

comm = comm.append(fixedParent.getMap().placeAt(fixedParent, fixedParent.getPosition()));

to

comm = comm.append(new AddPiece(fixedParent));

I.e., reverting the change in this line in r5723

This reversion makes this problem go away. Of course, it probably leaves the original problem un-fixed.