Connection problems in some play?

I've had connectivity issues with many games for a few days, some things work perfectly, like Minecraft and some steam games. However, in some games I can connect with luck only after 10 tries, then it also runs weirdly until I finish it again… When I download something, my internet runs weirdly perfect… Any ideas?

You may have an error in the port sharing of your router. The different games all use different ports and, for example, the Fritzbox guest access is limited and even blocks certain ports