From Tamron:
A notice regarding compatibility issue with the EOS 80D and availability of firmware update service
Dear users and potential purchasers of Tamron interchangeable lenses for Canon.
Thank you for using Tamron products.
We wish to notify you that the AF functions of the following interchangeable lenses for Canon, which have been produced before May 11st, 2015 and have not updated firmware when there were the firmware update service announcements below, do not function in Live View mode when used on the EOS 80D which went on sale on March 25th, 2016 in Japan.
*Please see the below links for the previous firmware update service announcements regarding the EOS Rebel T6s/EOS 760D (EOS 8000D) / the EOS Rebel T6i/ EOS 750D (EOS Kiss X8i), the EOS 5Ds / the EOS 5DsR, and the firmware update service for SP 150-600mm F/5-6.3 Di VC USD (Model A011) for panning shot.
http://www.tamron.co.jp/en/news/release_2015/0508_3.html
http://www.tamron.co.jp/en/news/release_2015/0508.html
http://www.tamron.co.jp/en/news/release_2015/0622_3.html
We sincerely apologize to all users and potential purchasers for any inconvenience the issue may cause.
Affected Models
Interchangeable lenses for Canon, which has been produced before May 11st
Serial numbers which have produced after May 11st, 2015
Firmware update will not be required for those lenses (serial numbers).
Please check the serial number from the links below.
For those who require firmware update service, please contact your local Tamron distributor for more details.