UBI has said flat out that it's a problem in Ranked

For context, this was about being put into a lobby with less than 10 players in a Ranked or Unranked match (5 v 4 situations), not about unbalanced matchmaking experiences (high elo vs low elo). Quick Match allows players to join in progress, so there should be options to have a full lobby. Ranked and Unranked do not allow for backfill.

But for Casual servers?

We don't have anything to share about changes to Quick Match matchmaking at the moment. This does not necessarily mean nothing is happening - it just means that there is nothing public to share. As mentioned in our matchmaking blog post, occasionally the system can have a hard time finding someone withing your MMR range and may have to expand the range to allow for faster matchmaking timing.
The team is aware of the examples that have been presented with Quick Match matchmaking balancing concerns. I have been linking... Read more

This is a reported UI glitch. The team is working to fix this in the future.