TP-Link archer C6 v2 EU 2.4 ghz not working

Check the wireless drivers. The C6's QCA9563/9886 should be using the non CT version. I think you should be using:

ath10k-firmware-qca988x
kmod-ath10k

Although apparently the drivers never really worked that well for 2.4Ghz so YMMV.

There are apparently work arounds for similar problems on the C7 v2 (QCA9558/9880) perhaps you could try?

The C6 may be best used without 2.4Ghz which is how I use QCA9563/9886-7 based devices.