Does the team meetingOnline externalId have an expiration date or reset after 60 days with other settings?

Question

Hello,

I have been creating meetings using the createOrGet endpoint.

Updating them using the externalId worked great until recently.

Now, when I check several of them through a GET onlineMeeting with the same userId/tenantId, I see that their externalId has become null.

Isn't the externalId supposed to be immutable?

Many thanks