Email notification links break chat history

### Description
When following an email notification link, some weird truncated view of the channel is shown, with no way to get out of it short of reloading.

### Steps to reproduce
- enable email notifications for some channel
- get mentioned in the channel
- follow the "View " link at the end of the email
- go through the matrix.to client selection dialogs, select Element Web
- you are shown a snippet of the discussion with a few comments before and after the mention. Click on the down arrow in the bottom right that's supposed to take you to the latest message.

You will end up with some truncated version of the messages (i.e. some of the messages are missing), with a page reload the only way of fixing it. This works even if the mention was recent enough that the latest message was already visible.
(A specific example: got mentioned in the next to last message of a channel, clicked on the link, saw all the latest messages but also a down arrow on the bottom right that had no reason to be there. Clicked on it, and the last ten or so messages disappeared.)

This happens often, but only the first time I follow a notification link; it cannot be reproduced by going through that link again.
Describe how what happens differs from what you expected.

### Version information

- **Platform**: web
- **Browser**: Chrome 89.0.4389.90
- **OS**: Ubuntu 20.04
- **URL**: app.element.io but also seen on EMS