Hello everyone i might need some help.

I am currently in the second year of my apprenticeship and i work on my own cnc lathe (BMG Mori T2) which is working great so far. My programs work, they are fast and percise. There is rarely a part thats not okay. There is only one thing bothering me and thats making threads in stainless parts.

I am from germany so i use the metric system. Everything below M8 breaks if i try to do a thread longer than 10mm and everything above just gets stuck and spins inside the tool mount until it tries to retrect which obviously would break the part if i wouldnt stop the machine. So far i stopped trying and just cut like 1-2mm deep to have the start of the thread. I would than finish the thread by hand afterwards which obviously takes up a ton of time. I can adjust the rotations/min while cutting into the material and while retracting. Is there something specific like more speed or less speed that could help me? I dont want to ruin more threading tools. We have the kind of threading tool that is seen in the picture.