Very strange, since no one else has reported this being an auto update. It's most unusual. I suggest you revert to the release channel, as this version is not on any thunderbird official download site, and there is no upgrade path for this release. The appearance is that 127 was downloaded and installed over 115. The URL shown in your screenshot is not an official download site. To revert, I suggest doing a backup for safety, reinstalling the release level over the top, and check for a compatibility.ini file that may need to be deleted.