Hi Alexander,
I moved to new version 26.5 and here my results:
Please see:
Test data(input/output/QGIS)
5371-Gml Gml.zip (55.1 KB)
Thanks,...Bug 5371: Gml to Gml- Conversion succeeded, output in QGIS -...like: Bug 5416: Gml to Gml- Conversion succeeded, input and output...