I have created and deployed bot using a sample bot Welcome-Bot example given in Azure portal docs. This bot shows a welcome message whenever the bot is joined or started. It shows welcome message when I test it on emulator. But when I deploy it to Azure and test in Test Web App chat or Teams it doesn't show me Welcome message. It show me the welcome message when I query something, i.e. it gives two responses : one is the welcome message and other one is the reply of the query asked .
For Microsoft Teams, you need to create an app manifest using App Studio and install in your personal scope.
For 1:1 bot conversation, ConversationUpdate event gets fired only for the first time. Only possible option to test welcome message is by installing your bot with a different user. For team scope this event is raised every time you install your app. You could test your welcome message in team scope if it helps.
Note: Here is how you can synthesize a fake event conversation update event and simulate the bot receiving it.
来源：https://stackoverflow.com/questions/55181264/msbot-not-responding-on-on-opening-the-bot-no-welcome-messaged-received