Hi Alexander,
I moved to new version 26.5 and here my results:
Please see:
Test data(input/output/QGIS)
5361-Gml Gml.zip (54.3 KB)
Thanks,...Bug 5361: GML to Gml- Conversion succeeded, output not open QGIS-...like:) Bug 5416: Gml to Gml- Conversion succeeded, input and output...