Welcome to the forum kbenzar.
Without access to the original ODT documents - and knowing exactly how you're importing your text (which importer, settings, etc.) - it's difficult to know exactly what's going on but I would guess that the situation you're getting is a consequence of the import function sharing styles between the text frames.
Depending on how you import your text, Scribus could be adding styles to automatically format the first text frame from the imported text, and then modifying the styles when the text is imported into the second text frame. Every subsequent import would modify the existing styles and therefore change the document formatting.
For example, if you import the first document which has a style "Heading" formatted to Arial 22pt and then import another document which has a style "Heading" formatted to Times 24pt, Scribus may - depending on how you import - just re-use the existing "Heading" style and change the formatting accordingly. This would mean that existing text formatted with that style would also change.
I would usually recommend importing text as plain text and applying the formatting manually in Scribus as required. This gives you full control over how the text is formatted.