Pion cannot connect with Janus without manually specifying Candidates SDPMid

[kenzoi]

Your environment.

• Version: v4.0.0-beta.9 (tested with v3.2.28 too)
• Janus: We don't control or have access to the Janus, we connect to a third party provider. (I assume that it is a Janus because they have on offer the line a=ssrc:xxxxxxxxx cname:janus)
• If it helps gather context I can paste here the offer/answer/candidate.

What did you do?

We receive an Offer which include the candidates. We send an Answer and then send the Candidates with ICE Trickle enabled.

We have two "clients" for this third party provider, one in the browser written in Typescript and one in our Pion stack.

What did you expect?

Connection between the peers.

What happened?

On browser everything works as expected and peers got connected.

On Pion we got an status of connection failed, unless manually specifying SDPMid as the string "a" on each local Candidate.