Sorry Martin, I misunderstand that.
Thanks for your answer.
Yes Cubase show 6 ms in the old project.
I tried now to change the buffersettings in UCX to 48 samples, and then I get 1.938 ms in output latency, and I can hear that the latency has improved a little on the VST synth, but I still can hear the delay between key and sound.
So the latency still affects when I change buffersettings up and down on the sound card, but it is way to long latency compared to normal use.
I only use Cubase own plugins that are included in the Cubase 9.5, except for the only extern VST I use, and that is Arturia CS80V.
I opened up the project I had the same problem with almost exact a year ago, and there were no Arturia VTS in that project, only Cubase own.