Subspaces are randomly empty in space hierarchy (over federation?)

[squahtx]

Description

When browsing a space in Element Web, the children of subspaces will randomly be excluded. Repeatedly viewing the same space will get you different missing children randomly.

I've looked at the network responses in the browser and rooms are definitely missing from the homeserver response, so it's not Element Web's doing.

Something to do with federation maybe? I've not noticed it when the entire space is on the same homeserver as my user.

Steps to reproduce

1. Create a space with lots of nested subspaces on one homeserver.
2. Using a different homeserver, eg. matrix.org, view the space hierarchy in Element Web repeatedly.
3. Notice runs of subspaces appearing with 0 rooms randomly.

Version information

• Homeserver: matrix.org: 8e8a008
• Homeserver: homeserver with spaces: 1.49.2