Cannot delete widget in web interface

### Description

I recently setup an internal matrix homeserver with riot-web attached. During first plays with the rooms I found 2 widgets (jitsi) that I cannot remove permanently.

Unfortunately, I cannot tell where these widgets came from. Yesterday there was only one widget that I added and that I could remove without problems.

### Steps to reproduce

- Simply click on *Remove for everyone* within the menu of one of the widgets.
- After confirmation in an overlayed dialog the widget is gone.
- Some (~20) seconds later a new dialog appears telling me `An error ocurred whilst trying to remove the widget from the room` and the widget gets reloaded.

Logs being sent: yes

### Version information

- **Platform**: web (desktop not tested)

For the web app:

- **Browser**: Firefox 73.0.1
- **OS**: Arch Linux
- **URL**: riot.aes-sb.de
- **Riot version**: using docker image `vectorim/riot-web:develop` (aka `d9fbbe16968c-react-2bf4513b44e7-js-21908aea6cb4`), same happens for the `:latest` image

### Additional information

Console log states
```
Failed to delete widget Error: "Timed out waiting for widget ID dimension-jitsi-1585408471205 to appear"
```

- It could be related to vector-im/element-web#9827 (which describes a problem on desktop, not web).
- Personal impression is that the problem is related with the riot app that was connected with the HS and that reported an open call all the time. The user (a colleague of mine, I do not know what he did exactly) reported issues there. [Potential issue](https://github.com/vector-im/riot-android/issues/3342)
- The room ID is `!BDLITNyAGlAbOgFLNl:aes-sb.de` that caused the issues