PLP1000 cannot achieve to have fast connection, around 90 Mbps

powerline devices are sensitive to interfernce. Even more so than what wireless is. 

things that can influence the speed: 

arc fault breakers

gfci outlets

surge protectors

cell phone chargers

cheap/poorly made electronics

electronics going bad

old/poor wiring

high draw appliances

Distance. The further away the devices are from each other, the slower they go. keep in mind, if the electronics are on difference circuit breakers the path has to go through the main junction box, increasing distance. 

Basically many things can impact powerline speeds. I'd look at tested reviews for powerline devices for actual performance numbers. They might be rated gigabit speeds but thats peak without any interference. for instance, check out smallnetbuilders speedtest of the pl1200.  optimal conditions had speeds around 400mbps but once you cross breakers, it drops down to around 100mbps. 

https://www.smallnetbuilder.com/lanwan/lanwan-reviews/32717-netgear-pl1200-powerline-1200-reviewed