I’ve been having trouble with Master documents in LO Writer; when I insert the subdocuments into the Master odm file, the spacing of many lines get altered related to original subdocuments’ meant layouts… Page size and margins set are exactly the same at all subdocuments and Master file, which puzzle me further! Any idea of how solving this issue?..
The central idea of master documents is being able to (re)define styles in one central place, so even if subdocuments (using the same style) have that style defined differently, the central definition from master document would override them all, and so would unify the styling of the whole result.
So it could well be that your subdocument has some style tuned to give some specific line spacing, but your ODM has the same style without the spacing?
Do you know the Relationships of the styles?
Relationships of the styles
It will help you gain knowledge to work with master document and sub-document without any problems.