'BadRequest' when send to specify groups - Bot Framework 4

Question

I have an issue with Skype Chatbot. I have integrated chatbot in my system, store group conversationId, serviceUrl, etc... in DB and send to these groups when needed. My system is using .NET Core 2.2 and Bot Framework 4 (version 4.7.0), the system worked well until yesterday. I have only 2 groups that cannot receive messages from Bot, the other groups still receive messages. My service throws the exception "Operation returned an invalid status code 'BadRequest'". These groups had received messages normal from the same Bot before yesterday. This is my issue. I try to update the Bot Framework up to the latest version (4.11.1), but the issue still not solved. I even remove this bot from these groups and re-add the bot again but still not work. Please help me explain and resolve this case, thank you. I have posted this issue in https://support.snatchbot.me/discuss/5fc8aeaf450c2201ac84b4b5