Hello ugo,
The problem seems to be related to the indirect order definition used in the file, instead of row/column index provided for each point.
At the moment such data representation is not supported (most likely, the support will not be included to the 1.7.3 update), so the solution at this point is to re-process the original scans in the native scanner application (providing that there's an option to use direct point indexing) or to re-save/convert E57 files in some point cloud utility that will add the direct indexing.