To test, use the LCD and click home all. Does the probe start flashing at any time? If so, your issue is very easy to fix. Run the following command from repetier host. M340 P0 S500 . Does the probe drop instantly? Next run M340 P0 S1500 . Does the probe raise instantly? Likely your issue will be with the first command. Change the S500 part to S600… now does the probe drop instantly?
If M340 P0 S600 results in a instant drop, you’ll need to adjust the firmware to reflect this change. In configuration.h search for a line containing M340 P0 S500 and change that to M340 P0 S600 then upload the firmware.
If you’re not sure how to upload firmware with arduino IDE, let me know and I’ll run you through it step by step.