In gcode, arcs use G02 and G03.
You should look at the gcode, look for G02/G03 and see if the First is set right. Maybe the postprocessor isn’t handling the unit conversion correctly.
Are there other kinds of curves that are that slow, or just the letters?
Microscopic slow sounds like a mm/s is being used for mm/min.
IIRC, the EstlCAM tutorial has you configure it to not use G02/G03, which makes it replace arcs with a bunch of lines. I don’t remember why that is though.