When you are using the Embedded WebChat control with DirectLine Bot service, it could randomly use WebSocket or Polling, which is randomly determined by DirectLine Bot service side. Once it is chosen, it will stick to that.
This issue could cause some activities that require WebSocket, not working, such as "Typing" activity.
A switch will be added to the embeded webchat in the next release. Please follow up this issue atthis link.
Before that, an option is to use your own client instead of the embedded WebChat control.