Around area:
N 52° 54.247', E 014° 10.859
the altitude are very wrong.
Whats the reason for that error?
Same here, it is some distinct area, but yes, data seem wrong, it is the data source. I use pure SRTM. Lidar often, but not sure if for this area. You may want to ask Sonny, he is here and on Twitter, he's very much into this. https://twitter.com/SonnyLidarDTMs?t=p64gDcPlWO2CIZtltMCZdg&s=09