Issue was that measuring usage of the storage system per tenant could fail, lead to the system thinking there was no room for more models.
This has been made more robust, and now fails safely.
Plan Limit exceeded means you're out of quota. This seems unlikely as it's set quite high.
2 issues may be related. I've seen some issues when Azure storage times out, when checking quotas. We should probably fail safe in this case rather than assume failure means the user is out of quota.