Blank widget outside of Element Web/Desktop

[aWeinzierl]

Describe the bug
When I pop out the widget on Desktop from chat.fosdem.org (website opens), it just shows a blank page.
When I try to view the widget in Element Android (1.3.17, 40103172, G-b5839, Gplay), first one or two green spinners appear, then the space becomes blank.
When I try to view the widget in Edge or Brave the same happens

To Reproduce
(Element Android)

1. open Matrix.org Foundation & Community devroom
2. Tap on the widget button with 2 as indicator
3. Select the schedule, and see a blank page soon
4. Tap the three dots at the top right
5. Tap open in Browser
6. see green spinner in Edge, then the website goes blank
7. copy the url
8. open Brave and open the url, see a spinner and then a blank page again

(Desktop-Browser)

1. open Matrix.org Foundation & Community devroom
2. Pin the schedule widget if not yet pinned
3. see "No events scheduled" in the widget after short loading
4. "Popout widget"
5. see blank tab opening

Expected behavior
see "No events scheduled" in the widget after short loading whenever a blank widget is shown

Screenshots
Screen of Element Android:

Desktop (please complete the following information):

• OS: Windows 10 Pro 19044.1503
• Browser: Edge
• Version: Version 98.0.1108.43 (Official build) (64-bit)
• Element FOSDEM 2022 version: 1.10.1 Olm version: 3.2.8

Smartphone (please complete the following information):

• Device:Fairphone 3+
• OS: Android 10
• Browser: Edge; Brave
• Version: 97.0.1072.78 (Edge);1.34.81 (Brave)

Additional context
The live stream widget works just fine everywhere