@LordCatzorz For the organization I work for, it stopped around January 15. I've contacted MS support and they had me try a few things and one thing that seems to work is creating a custom messaging policy from Teams admin to have the Read Receipt turned on by default. You will need a Teams admin to make this change. This would work if we wanted to force read receipts for everybody, but we want the users to make this choice on their Teams setting.
They also wanted me to make changes in the ADFS Sync process, but I don't think that has any impact on the issue since the custom policy actually makes the read receipt work. The recommendation for the ADFS sync was to clear the SRV attribute, which we don't have or use, and then perform a delta sync.
The fact that the custom policy works makes me think that there were Teams messaging policy changes that happened in the backend made by MS that broke something. Nobody made changes to the default Teams messaging policy from our tenant. So, my theory is the issue is that the default Teams messaging policy broke for some tenants because of some changes from MS that we are unaware of.
