I’m not sure this is intentional or not, but something you really need to pay attention to if you develop search based solutions in SharePoint Online (afaik it does not impact search for on-premises).
Up until recently(?) all managed property names were case insensitive. The change now is that automatically created managed properties based on site columns (https://docs.microsoft.com/en-us/sharepoint/technical-reference/automatically-created-managed-properties-in-sharepoint) – those ending in OWS<something>, are now case sensitive. The others work as before.
If you for example create a site column of type number named MyFoo, the automatically created managed property for this column will be MyFooOWSNMBR. Previously you could retrieve the value of this property, or query it by entering any casing of the name.
This meant that MyFooOWSNMBR:10 and myfooowsnmbr:10 were equal queries. But not any more.
If you use any casing but the one listed in the search schema it will be treated as an unknown managed property yielding no results or values on retrieval.
Which means if you are like me and typically type all managed property names in lowercase you have work to do to fix it all up.
This information was found at https://github.com/MicrosoftDocs/OfficeDocs-SharePoint/issues/296.
