So a 1 gig plan can't handle 2 devices and just streaming a movie?

I mean legit I have 2 devices running on my modem that is putting out 110% and it still will buffer when im watching a movie. All I do is stream. I dont use a VPN, I dont download and I dont game. I really dont think im putting too much pressure on this modem and im like within 20ft of it all the time. I dont need an extender or a technician to come over, it is working but your internet is just slow.