First thing to check for all drivers.
Make it better with the help of software Driver Restore. Software automatically checks all the necessary drivers and all updates itself.
Download: Driver Restore
If the drivers are installed go further.
Lagging in the UnderRail can be associated with a bad optimization of games for your PC.
Fix this problem, you can use the patch fix for UnderRail. Powered by Steam and cracked game.
Installation: Install the game folder.
After installing the improved optimization UnderRail for different PC system. Enlarge FPS and disappear lags, freezes, stattering.
Good luck, hope UnderRail you enjoy.