Why these lags?

Hello,

I downloaded Fortnite again after a long time, and everything worked fine at first, but after two days it started lagging slightly. I restarted the router and it worked again, but not for long. Since then, nothing has worked. The game takes an incredibly long time to load, and the lag is unbearable. I keep seeing an icon, see image. My computer isn't connected directly to the router, but rather to an amplifier via a LAN cable. The router is practically two rooms away.

I've tried a lot of things, from updating the driver to lowering the graphics settings. I've also made a few changes to the game, but to no avail. According to the speed test, the ping is good.

I hope someone can help me.