@RainerSchleicher Welcome to NGA and to the Rose Forum ..
You don't say where you are growing your roses ... you can update your profile any time. The only reason I am bringing that up is that it gives is an idea of the kind of climate you have for your roses.
@pjnew is right on about this rose needing more water. The brown leaf tip in the first photo is an indicator of water stress.
Water stress can be caused by under watering, root competition, or by fast drainage. If the problem is caused by fast drainage, that means the water you have applied to the plant is moving through the root zone too fast for the plant to take up the moisture it needs.
Not all roses have the same water needs. Some roses are more thirsty than others, so you need to adjust your watering accordingly.
There may be other issues, but water stress appears to be the obvious problem in your photos.
I hope this helps.