Hi Lucie,
Thanks for your update.
Still we couldn't able to reproduce the issue as you mentioned. Waiting popup is working fine when panel/lable is place inside it with some custom width. Attached is the sample in which we tried to reproduce the issue.
WaitingPopupF_Forum60185.zip* In our sample, Waitingpopup is placed inside the Multipage whereas Multipage is integrated with TabStripItem.
* We have placed the WaitingPopup inside the Second Page of Multipage.
* We invoked waitingpopup once "Show Popup" is pressed.
If anything we made wrong in reproducing the issue please correct us.
Let us know if our sample helps.
Regards,
Gokulkumar B