“EKF goes crazy” means that the position estimate goes far off and the vehicle suddenly moves horizontally or does it means something else?
One thing that looks suspicious is the number of satellites is dropping a few times.
The GPS also seems to be switching between RTK float and RTK fixed. I wonder if it might be good to test with no RTK GPS and see if it behaves more reliably. That would at least point to whether the problem is with the RTK or not (although I suspect it is).
The GPS seems to be reporting regularly (i.e. regular 5hz update rate) so if it is the GPS then the issueis within the data from the GPS…