Why on my lathe G61 does not work on circles?

I think this is almost certainly a side-effect of M2:

linuxcnc.org/docs/2.7/html/gcode/m-code.html#mcode:m2-m30

You will see that M2 re-sets the plane to G17. (I know,this is very much not what you want on a lathe, but this is probably what the RS274 standard says that M2 should do)

If you are using CAM software you should be able to force it to always add a G18 at the top of every file. Or to not but an M2 at the bottom.

Thank you.
Yes, I already did it.
I checked the other programs that were runned out correctly.
everywhere there was a preamble with G18.