No local position preventing copter from going into Position Hold

Relevant log file review: https://logs.px4.io/plot_app?log=9eaf8e64-6e7a-46f8-9c24-17c957b06d46

Why is there an error “Failsafe enabled: no local position”? What are the conditions when such an error might be produced? We are sending position data telemetry and using the EKF2_AID_MASK parameter to accept the data as vision position.

Also, I followed the instructions in Redirecting to latest version of document (master) and generated the pdf plots. In those, for some time the horizontal position innovation goes constant. Why is that? Here is the pdf: log_135_2019-5-30-18-31-28.ulg.pdf (127.3 KB)

Any help would be much appreciated!