today I upgraded to version 6.12 and openvpn didn't work.
The flags of the CA and the router certificate after updating was only a big "T"
After I deleted the certificates (CA and signed certificate for router) and imported them again everythings works as expected. <== (I didn't do this step in 6.11, maybe it works also here???)
The flags are: for CA = "AT" and for the router cert = "KT"
So, the option "Require Client Certificate" in version 6.12 works.