I do not fully understand what transpires when using a flash drive to save Word documents but, others profess on this forum to NOT use a flash drive on Word files. Apparently, it will corupt the file and cause problems such as yours.

When the other posters come online hopefully they will offer more details. In the interim, you can search this forum for FLASH DRIVE and you may come up with the details they offer.

Sorry I cannot be more informative.