in my editor my imported notes have like spaces that don't take up space? like two words are run together so that search no longer works but if you cursor across it stops 2 times in this null zone - is it possible to globally replace these nulls or whatever they are? thanks.
once you know what the character is, you may be able to use regex find/replace in the markdown editor's search bar to quickly replace them with normal spaces
If you copy a section of text that contains these characters and use the site suggested by @bwat47 (above) it will tell you what each unicode character is, such as this zero-width space example.
Normally the Joplin built-in importer is more reliable. With these broken notes you seem to have and all the duplicates, would it make sense to delete everything and re-import it again?