Error on initial sync and initial sync filter discarded

[t3chguy]

Steps to reproduce

1. Open develop.element.io
2. Login to matrix.org
3. Observe error

Outcome

What did you expect?

No errors, initial sync filter to be valid & apply

What happened instead?

Regressed by matrix-org/matrix-js-sdk#2726

Operating system

No response

Browser information

No response

URL for webapp

No response

Application version

No response

Homeserver

No response

Will you send logs?

No