Originally Posted by
Octane
The other aircraft in the vicinity on the same route remained on screen until landing.
It's likely then (see explanations above) that the aircraft that remained on your screen was sending ADS-B data (and hence only needed to be picked up by one station on the ground to establish its position) and the aircraft that disappeared was only sending Mode S (and therefore could only be plotted while being picked up simultaneously by several ground stations).
Nothing to do with being blocked (in that case, FR24 wouldn't show the aircraft at all).