I have found the issue:
XML/GPX files cannot have & without being changed to &. This is done for almost all the fields in Cachly for a GPX export, but the <name> field normally contains the GC Code. However, in your case it seems that GSAK inserted the Waypoint name into that field.
For now, you can change the & to & in the file, and I will put in a fix for our 7.0.7 version of Cachly.