I used the DfuSe V3.0.3 tool (from ST Microelectronics) to upgrade the Mountaineer Eth firmware from 4.2 QFE1 to 4.2 QFE2. The tool crashes at the beginning of the verification step. The firmware upgrade itself went fine.
I am aware that the docs mentioned an older version of DfuSe (V3.0.2), but this version was not available from the STM website.
I am posting this information here in the forum only so that the Mountaineer Group can track this issue. I don’t expect an answer if this is only a bug with the DfuSe tool.