I am having some of the same range problems suddenly. I've been flying the P3S for weeks and I have had no trouble getting a thousand feet of range, but in the last few days (which included firmware update 1.8.10), I have absolutely atrocious range, flying in exactly the same area. I can duplicate the problem just by hovering about 250 ft away, at 200 ft altitude, with very clear line of sight. I'll have 4 bars one instant and then two bars or even one tiny red bar a few seconds later, lots of Weak Signal messages. It jumps around, and if I point the RC away, it will disconnect with Signal Lost message and RTH. I don't see anything unusual with the WiFi Analyzer. Everything works great when I get within 50 feet. Everything solid as rock on the ground.
It could be a lot of things, and I'm not ready to blame it on the firmware just yet. More tests needed.
Today everything seems decent again. I ran a Litchi Waypoint mission and kept RC connectivity as expected throughout most of the mission, just as it has done in the past. Hmmm.... Maybe it was temporary interference after all.