I don't do BIF. But I am under the Impression, that my Tamron 100-400 works fine on both my cameras the EOS M5 and the EOS 6DMII.
As far as I have seen Firmware Ver. 2 should have dealed with some IS issues. Have you updated the Firmware on your lens?
Just recently I send mine to Tamron for Firmware update as I do not have the TAP in Console. As it is my only Tamron lens so far, it is cheaper for me to send the lens to the Tamron Service (~6 Euros, instead of paying ~70 Euros for the console).
Unfortunately I send it to Tamron some days before this announcement of Ver. 3. Now I do not know if I already have Ver.3 flashed on my lens.
Does anybody know, if I'm able to find out the Firmware Version on my own without having the TAP in console?