Hi!
This definitely looks like a javascript issue, since it’s working until you interact with the select box. An event handler is most likely connected in an incorrect way and it interacts with the search plugin as well. This can come from 2 places: 3rd party plugins or the theme
Since you tried to disable all the plugins, then the only thing left is the theme. There must be a file which is loaded by the theme. Try to switch the theme temporary, and the problem should go away immediately.
Let me know how it goes.
Best,Ernest Marcinko
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