I can save configurations, but I'm not able to read and load saved configurations. My fault?
If you mean saving the current output config as default settings (Ctrl+Alt+D), which writes it to defaultSettings.py in the Avidemux profile directory, a file which will be read and executed on the next Avidemux startup or anytime with Ctrl+R, then this works fine for me with 2.7.3 VC++.
Loading saved video encoder profiles within x264 and x265 configuration dialogs is broken with VC++, this has been recently reported in the German section of the forum (https://avidemux.org/smif/index.php/topic,18659.0.html).
Use a MinGW build (either a private one from the topic https://avidemux.org/smif/index.php/topic,18653.0.html (https://avidemux.org/smif/index.php/topic,18653.0.html) which will be deleted by WeTransfer in a few hours or the official 2.7.2 190310 win64 one from https://avidemux.org/nightly/win64/ (https://avidemux.org/nightly/win64/)) if you need a fully functional Avidemux without VapourSynth support right now.