I need help with something please

[paragon]

Hello guys, so I have made a private server and just been developing it locally and that's all going well, however, Someone under my same household tried to login because we were going to play and I set it in the config and stuff and they were able to login to the server, the problem is on their pc the game is like stuck in this super speed mode, everything is super fast, even when logging out it usually takes 30 seconds to camp on their pc it takes less than 5 seconds. The game is completely unplayable on their pc, I directly created a copy of my RoF2 client and copied it to their pc via USB. they got modern specs, so like new GPU and CPU. I'm assuming that is what is causing this issue? if anyone knows how to fix this please let me know