I wouldn't of thought ramp up time would cause the issue, especially since it seems to get up to 10k OK.

However, we really need more details.
VFD make/model (there must be a sticker on it somewhere..), what software/controller is the machine using, and how is the VFD interfaced to the controller (0-10V or Modbus).
Any messages shown on the VFD when the spindle stops?