The master document function in Word is defective and likely to destroy your documents. It is better avoided altogether. Combine the documents into one larger document. The Insert Documents add-in on my web site will help with that, or you can use Insert Object > Text from File

__________________
Graham Mayor - MS MVP (Word) (2002-2019)
Visit my web site for more programming tips and ready made processes www.gmayor.com

I read about this just yesterday, and also many years ago. Does Microsoft not have time and resources to fix the problems and improve Master Document.