Just to check if it's related to the spellfix extension, could you open database.sqlite in an SQlite browser, then set "db.fuzzySearchEnabled" to "0" in the "settings" table. After you do that, does it make any difference? (after you're done, don't forget to set it back to its original value, probably "1")
Also is there any errors or warnings in the console? https://joplinapp.org/debugging