Hi Alexander,
I moved to new version 26.5 and here my results:
Please see:
Test data(input/output/QGIS)
shapefile8.7z (7.5 MB)
Please make conversion in your side from Shapefile to Kml and test it in your side in …... Reduce the KML size Export only needed attributes – disable...disable attribute export or select a subset of fields. Simplify...