With I open some of my Private Space apps then I click back to return to the apps list, the stock launcher, including only the apps in Private Space, is displayed, even if I use other Launcher (Niagara) in my normal profile.
I have tried to change to the stock launcher in normal space and the issue still persist when I open some apps in PS.
This occurs for some apps, specially for MiDGT app: https://play.google.com/store/apps/details?id=com.dgt.midgt
(you can test without any account: only open in PS then click back 2 times to exit)