The problem is originated in a theme script, which removes input placeholders, and replaces them with labels. It makes changes to the search input structure like so: https://i.imgur.com/cW6GRp3.jpg
The problem is coming from the /wp-content/themes/salient/js/init.js file, probably from lines 13868 and 13869:
These function calls are removing the placeholders (there might be more, I only found these). A possible solution would be to either remove or comment these lines in that file, like so:
That will most likely solve the problem. In case you want to make changes to the file, I highly recommend having a back-up of your site before doing so, in case anything goes bad. For further information, you can also contact the theme developer as well.
I hope this helps!Best,
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