Teams bot message events not received by our web service

Hi!

We are experiencing a strange problem with our Teams bot. For messages sent from one of our customer's tenant (and one tenant ONLY) we never receive any of the events with type `message`, `messageReaction`, or `invoke` on our web service, and only receive `conversationUpdate` events. For all other tenants it works without any problems.

This makes me think it might be somehow related to some tenant-specific configuration, but I was not able to find any information about it anywhere.

Did anyone experience something similar before?