Advanced Search not working- my syntax must be wrong

I have a couple of documents I know has phrases in them but I must be getting the syntax wrong on the search and need some guidance, please.

Here is my search:

"xxx xxx xxx" AND "xxx xxx xxx"

I have also tried

("xxx xxx xxx") AND "xxx xxx xxx"

neither of these are finding the documents in X1. When I eventually found them I verified that both phrases were in the documents so I am not sure why X1 is not finding them.

Anyone have any ideas?

thanks
steve

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