Problems with custom kinematics

Hello. 
I have a master degree project that is connected to linuxCNC (I am developing a custom robot). 
I have cartesian kinematics and Remote Center of Motion kinematics combined. 
Everything moves perfectly etc. 
However, there is one problem: RCM allows to change probe's orientation in 2 planes: X and Z. When I send the command to orientate the probe 60 degrees (for example) both joints move according to set speed. But when I tell the robot to change probe's orientation to -60 degrees, A joint requires to rotate 180 degrees and does it at around 360 degrees/min (incredibly slow) (C joint rotates at the set speed). 

And so, when I change the probe's orientation from 60 to - 60 (or from 30 to - 30, doesn't matter), One joint moves at set speed, but the secondary joint needs to make a half rotation at very slow speed.
Changing speed variables in .ini file did nothing. When in joint mode, I can control the speed of both joints. It only occurs when applying kinematics.
is there a way to increase the speed of actuation?
Please help, if anyone encountered such a problem.
Sincerely