Onedrive on iOS sends some docx files to open in Word

Hello everyone. 
I have the Onedrive iOS app v16.19.8 installed. Lately, I have been working on three documents, which are modified copies of a fourth document. After Autosaving them, I tried to preview them on the app on my iPhone 15, and where 100% of the time the app would preview the document in an uneditable inherent viewer, these documents, and subsequently some other files, are viewed using the DEFAULT system viewer or it opens in the Word app I have installed. 

I require your diligent assistance in resolving this issue in the most efficient way possible. 

I can also attach screenshots if necessary. 

Many thanks.