How Autocomplete search work?
The autocomplete is built to work within the dropdown. So the fuzzy search of autocomplete only works within the dropdown as expected. you can choose your result from the dropdown as this is the expected behavior but as soon as you press enter it will not show the result as shown in the dropdown. Because the dropdown uses advance search and show result like post, taxonomy, and meta so pressing enter means showing and selecting all of that from the dropdown which is not possible.
So, at this moment when you press enter it does a very basic text search to check if the string match from the beginning. You can add some description there like asking your user to choose the result from dropdown instead of pressing enter button or use our basic text search instead. The basic text search is not as smooth as autocomplete but it provides the result appropriately.