Apple Macbook 2012 not connecting to 5GHz AC

I have a CAPSMAN network of around 5 APs, in tunnel mode, and is working fine with both 2GHz and 5GHz networks (for most devices except a Macbook 2012 on 5GHz).

The Macbook can connect to the 2GHz network but not the 5GHz.

All other devices (iPhone 7, iPad, Windows laptops etc) can connect OK on both 2GHz and 5GHz.

For CAPSMAN 5GHz provisioning the supported mode is set to AC only, would this be why the Macbook cannot connect?

If i include additional supported modes so that the Macbook 2012 can connect, what should these modes be and would it affect the speed of the AC devices?

Thanks in advance

If it is set to AC only, it will not work, as 2012 devices did not support 802.11ac yet