Site’s search function returns different results between devices?

I received the following email from a site user who is using the WordPress search function at the top of any page on the site to search for posts within the site:
“I am able to search for a topic using quotation marks around the terms and it works fine on my PC.
But when I try the same search string on my iPhone, I always get the “Not Found” message. On my phone I have to remove the quotation marks, and it works but with a lot of other results.”
Any ideas what might be going on here?
Seems odd to me that the search function would return different results between devices?
THANKS!

• This topic was modified 2 years, 4 months ago by Jan Dembowski. Reason: Moved to Fixing WordPress, this is not an Everything else WordPress topic