B3rni wrote

Can the Enviroment between the two CPE´s cause such behaviors?

No. Throughput (or rather goodput) of the wireless link looks pretty good, except that you probably can boost it by turning MAXtream off. MAXtream TDMA is useless on a PtP link. Also make sure to select 802.11n-only mode, 40 MHz channel width and a correct Distance setting (set to either »Auto« or to the real distance + 0.1km). I guess you have already aligned the CPE's antennas to each other, but it might be worth to check again using the Antenna Alignment tool.

To test pure Ethernet goodput, use iperf running on a server in the local network of building 1 and a laptop in building 2. The built-in test of the CPEs uses iperf, too, but only measures wireless goodput. See https://iperf.fr/.

As for low throughputs to/from an Internet server this can have many causes such as network load, server load, routing issues, unreliable test methods at the test site etc. I don't trust such »speed« tests (which are in fact tests of throughput at a given bandwidth; speed of electrical signals is always the same, a physical constant). Thus, to test the throughput you can achieve over an Internet uplink for a given service (file downloads/uploads, web surfing, VoIP etc.) just use the service to measure its throughput.