Lost WP rover firmware


I use the Matek F765-WSE motherboard with M8Q-5883 GPS in a feeder boat.
It has Rover 4.2 firmware, but the same problem exists on the previous version as well.
I go out to a new place, delete all the previous WP, then save the new WP on the new lake.
I will add a new WP later, it appears to be saved on telemtria, but it disappears on the next restart.
from here on, only complete deletion works and the points must be added again.
What causes this problem and how can it be solved?
Thanks for the help