This is quite common.
Normally you have to work over igs files until they are ready to work with. It depends on what you need from them
You can ask translator, or import options to automatic sew and optimize.
I prefer to do it manually.
Firts optimize surfaces with Synchronous, and then start sewing (depening on your part this could be really ast process or it could take hours...)
Use Examine Geometry to check if your part has "open" sheet boundaries while sewing.
Hope this help
Oh, just Notice:
First of all: when importing this kind of files (I mean, as I can see, it looks like an assembly) igs un-check "Flatten Assembly" so your part became multiple components.