Thanks, that is perfectly fine.
The issue is with the response from the server. There are two empty lines added before each ajax request (including the search and all other WordPress core requests). It is hard to tell where the cause is, usually it’s either a 3rd party code that hooks into page outputs (like a cache), or somewhere somehow a file was copied incorrectly. I don’t know if it’s worth looking to find the cause and fix, it could take hours.
The search query already has an auto-fix within the script for this, to remove empty lines and characters. Somehow we forgot to add that to the autocomplete part, it never came up until now.
There is a new release scheduled for the next couple of days, I will implement a fix for it, and hopefully that should bypass the empty lines issue, resolving the problem.