It seems that a new minor bug has appeared with FP4 for Domino 8.5.3: SearchView HTTP action will return error 500 after installing Domino 8.5.3 FP4.

What happens is that searches made at a browser by using a URL including the operator  SearchView get an error 500.

To solve it, just uninstall the FP4 by launching the FP4 installer again.