in a new (verified) session on element, all earlier messages from verified users appear as unverified

### description

after logging in on https://app.element.io/, all earlier messages coming from users that have be verified by cross-signing (including myself) appear with a grey shield with a description saying: “the authenticity of this encrypted message can't be guaranteed on this device”.

previously, i added new sessions on riot (web or desktop), and all messages appeared the same. is it something new from element 1.7? since they are verified by my other sessions, could they appear as verified on this new one too? i would prefer all messages to appear the same on all sessions.

### steps to reproduce

- with cross-signing set up with multiple valid session on riot web, riot android, riotx and riot desktop, sign in on https://app.element.io/.
- verify your new session from an existing one.

all earlier messages coming from users verified with cross-signing appear with a grey shield. messages coming from non-verified users appear without a shield.


it would be better if all messages would appear the same in all sessions.

logs being sent: no

### version information

- **platform**: web (in-browser) 1.7.0
- **browser**: firefox 78.0.1
- **o.s.**: ubuntu
- **u.r.l.**: https://app.element.io/
- **homeserver**: synapse 1.14.0