Hi All
I had the same issue in the last days: roughly I could download a copy of a
website in August and it was displaying well.
I tried a few days ago to download an updated copy but the offline copy would
never display correctly. One css resource was not loaded correctly.
I finally tried deleting the WildcardFilters.txt file in the HTS folder and
that solved my issue. 
I hope this helps someone else.

By the way, HTTrack is an excellent software. I tried others of the same type,
and could only go through the authentication of the website using HTTrack.
Thanks a lot for it!