the issue likely resides in an application called Smart Actions. To verify that this is the issue, look for it under system settings/ Apps/ under "running". If it is listed under "running", it is likely causing the issue (it was for me) .
To turn off the auto reply, select or navigate to the Smart Actions app and open it. There will be an icon listed below "Meeting". Touch screen "Meeting" and under the "Actions" list, unplug the "Auto Reply Text" battery icon by sliding it from left to right. Touch screen "save" at the very top of the screen and the issue should be resolved.
If you don't have this particular Smart Actions app, it is likely something similar by a different name which manages things like battery consumption or power management type applications.