Bad ping despite good internet in Fortnite?

I have a problem, in Fortnite I always Ping 20, then for 5 min 100s, then for 1 minute again a good, etc. Actually, my internet is quite good? Even made a speed test during the 'high ping' phases and it came out:

Latency: 12ms

Download speed: 97.00

I tried a lot, deleted Antivirus, cleaned Lankabel, restarted W-Lan Router, recorded replays in the game and turned off my cell phone Wi-Fi. Neighbors / family can't lie, the neighbors do not use our internet and as I said, 12ms according to Speedtest so no idea, on the Internet it is certainly not.

(Play on the right game servers, and if I'm still streaming 12-15ms according to speedtest, happens outside of streams btw)

Maybe you have performance problems in the line. Which provider are you? This is often the case with Vodafone. Stream often over twitch and have the same problem. Best directly call the provider. Or. Check sources of interference at home.

I used to do the speed test while doing a 100 ping, and 14ms came out, so I guess it's not the Internet provider. Am with cable Germany btw.

Does not mean anything, since the aborts only a fraction of a second go. The speedtest does not show that.

Ok, then call tomorrow at which. I'll get in touch

Wow, they just say it's not where they are… What am I doing now? Playing the whole holiday with 100 ping phases or what?