After confirming with the team, I have some things to share.
First of all, the platform does attempts to remove the C:ProgramDataPackages{appName}<userSid>SystemAppData folder at package uninstall, but like other file system locations, the remove is best-effort basis, i.e., even if we hit an error we don’t want to fail the uninstall. So you should only have an empty C:ProgramDataPackages{appName}<userSid> folder left after uninstall.
Cleanup of this per-user folder happens when the current user is being removed.
It is safe to manually delete the empty per-user folder, if desired, but it requires admin privilege.
If the existence of an empty and harmless folder is not causing any issue, then there should be no problem.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…