Bad internet despite 100MBits line?

When playing Fortnite the game keeps stalling and it is shown to me that the internet is bad even though I have a 100 Mbit line. I get the internet through a DEVOLO550.

I've already tried this:

1. I have already connected the Devolo to the PC via radio, no change on the Internet.

2. I then connected the router directly to the PC, then the result from the internet was much worse.

3. I have already updated the DEVOLO.

100 Mbit connection means nothing.

I would measure the connection:

https://www.wieistmeineip.de/

If everything is OK, there may be a hardware problem.