I use the same XML settings on Windows to export Colmap+masks. But on my Ubuntu computer, I got an error with RealityScan 2.1.1
Hello @gaojing418 thank you for your report. We already have this one in our bug backlog.
The public link is here: https://issues.unrealengine.com/issue/RC-3296
The workaround is to use PNG 32-bit BGRA.