Word download in Rise not downloading

Hi all, i'm hoping you one of you may be able to help me with an error i'm having on Rise.

I've created a Rise module which hosts a few .docx word documents. When I tested it it all worked fine, and I did this via mac, pc and mobile phone.

Now that it's live, we've had a handful of queries from users that they are getting  this error message:

"The file (name) cannot be opened as there are problems with the contents"

Has anyone seen this before?

My gut thinks it's a compatibility issue with older versions of Word or even the browser being used to access Rise, but as the learners are all external, it's hard to obtain feedback.

Thanks

Rach