Here is a list
with all fixes we made between Sitefinity 3.7 SP3 and 3.7 SP4. There are no other changes to the search engine that the fix I told you about.
You can check App_Data/sitefiniy.log for some related errors. You could have something on your pages or content item content that breaks the search. Controls that use session and forms authentication methods breaks the index service if the logic is not escaped from the crawler request.
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