Figured out the problem, the downloaded file from the ASUS website was: UL-ASUS_T004-TW-11.2.5.26-user.zip but the ASUS documentation says it should be in the format of: UL-A86- SKU-xx.x.x.xx-user.zip
So I changed the file name on the internal storage to UL-A86- SKU-11.2.5.26-user.zip and autoupdate was available after a restart.