Hi @ThomasDaheim,
According to the OES code it should be the the dataset from your link (SRTM CGIAR v4.1).
I was basically clicking random points around mt. everest in your app 
to see when the height changes.
If it is the same resolution the difference is probably due to the CGIAR post processing of the SRTM data. I think the problem with the original SRTM data were a lot of data “holes”.
We deemed continous data more important than exact height.
Of course the difference is quite significant sometimes, but as the resolution is 90m you won’t get exact data for every point anyways.