Using Solidworks 2017 Service pack 4.1 the sldasm files only partially import. Instances, folders, and suppressed parts also mess up the import. Suppressed parts show up from different configurations and mates from those configurations affect parts. Instances of parts from arrays are also discarded in the process.
This issue has been reproduced and tested in 4.19.2 (0.182) and 4.20.2 (4.20E2)
Results: The sldasm files only partially imports assembly data
Expected: Assembly data is fully imported
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-63335 in the post.