PUBG is a ton of fun, and it also has a ton of problems. Here's an easy way to improve your frame rate.
Disable your Game Capture! Game Capture is what allows you to record gameplay footage while you play, so you can show your friends online, and say, "Hey! Look at me. I'm playing a videogame!"
Game Capture runs in the background, and apparently it is disturbing the smooth FPS of your gameplay. Just go into the main menu, choose "Settings", then pick "Preferences". Select "Allow Broadcast and Capture" and disable this setting.
Once you do this, you won't be able to take screenshots or video, but trust me, no one cares about your screenshots or video. It's like taking video of a concert. All you are doing is being annoying while making a video that no one will ever watch.