The root object is missing or invalid error

A few employees have reported problems when opening some documents. 2018.011.20055 version shows "The root object is missing or invalid" error. A bit older 20035 version shows "There was a problem reading this document (14)". But i can open such document with Chrome and even older Reader XI version or Acrobat 9 version. So, it seems there is some problem with a document, but recent Reader versions are more affected by this and can't open it. Is there any way to avoid this, maybe some update can make Reader more accepting/ignore such errors. They seem like a minor thing as document looks perfect in Chrome or Reader XI. I can't share any document as they are private and i'm not able to reproduce it myself with some test document. Last document that i saw has "Merged" in its name. It looks like a few paper documents were scanned and then separate pdfs merged with some tool into one piece. Probably that tool does something incorrectly when merging.