Shared library – thumbnails

So I’ve read a number of threads and still can’t seem to find a workable solution. All my movies/series are on my NAS. I have one RPi set up as my scraper that updates the SQL db on the NAS. I haven’t been able to get the thimbnails working on the other machines though: a 2nd RPi and an Android TV. I exported the library with separate files to their sources on the LAN under the impression that the other machines would source the thumbnails from the NAS rather than scraping the internet, but this doesn’t seem to be doing the job. I’m not trying to have a shared thumbnail repository as that seems to be frought with danger, I just want each machine to have its local store of thumbnails working. Any pointers?