FPS drop / Game-lag is influenced by different factors like heavy system load, intermittent network drop, high server load etc.
We can try the following - you don't have to try them all; just work your way down the list until you find the one that works for you:
1. Close the network- hogging programs:
You may see network lagging issues on your game if there're programs taking up a larger bandwidth of network resources on your computer. Check your computer and close the programs you don’t need and see if the network status of your game becomes normal.
2. Temporarily disable the firewall:
Firewall or antivirus software may cause interference to the network connection of your game. You can verify the same by temporarily disabling the firewall (refer to the firewall documentation for instructions on disabling it).
If this resolves your problem, you can add your game to the white list of your firewall. Please contact the vendor of the firewall and ask them for advice.
3. Reduce the heat of your computer:
You may get low FPS or lagging issues if your computer is overheating. Check your computer and see if its cooling system works fine. Clear the dust on the cooling system and the vents.
4. Lower your graphics settings:
You can't get a smooth gaming experience if the graphics settings on your game put a heavy burden on your computer. Try lowering your graphic settings for your game and check. Go to the graphics or display settings of your game, then experiment with the lower settings and see if this helps you fix it.
5. Update your drivers:
You may get the lagging issues with your game if you're using Microsoft's generic device drivers or if the drivers are out of date. Please update your drivers and ensure they are the unique manufacturer's driver when applicable and not a generic version. You can download the latest [NVIDIA] or [AMD] GPU drivers from its support pages.
If the issue persists, please contact PUBG Player Support with a brief description of the issue along with Match ID (session, where you experienced FPS issues) and replay of that match.