Question on Geom App

[parisse]

I can not answer without the full construction. It might be because of rounding errors (with numeric data) or because you are using symbolic data that are not automatically simplified in is_perpendicular.
If you want more info, try your figure with Xcas in a geometry 2d level, then use the Save commandlines in the Fig menu to save the commandline in a file and copy/paste the content of the file, that way I can easily reproduce the problem and help you (unfortunately the Prime does not provide a similar feature to save/restore a figure from commandlines, you must use Xcas for that).