Can you please update your ticket with temporary FTP and log-in information? I'm guessing the issues might be related to a higher level caching, but I cannot investigate unless I'm able to debug through the code.
1. It happens when the ajax request fails for some reason: termporary server outage, internal error, php fatal error. Removing the JS part will not solve the actual problem, that the ajax response is failing.
If it's irregular, and there is no certain search phrase causing it, then it's definitely a server related problem, which usually goes away once the server is stable again. If it was a php error, it would be re-creatable by entering the same search phrase and getting the error message every time. If that is the case, let me know what phrase(s) are definitely causing the error, and I will be able to get to it via debugging.
2. Make sure that the keyword exceptions are not entered into the first option on that panel, but to the second one Keyword exceptions – replace whole words only: https://i.imgur.com/f5D9TYr.png
If you enter those words to the first one (replace anywhere) then even partial matches will be replace, therefore for example the search phrase “Transferencias de” will become “Trnsferencs” which will probably return 0 results.
3. And are they still not showing up? If the word length is now 1 and stop words are disabled and the index is re-created it should be working fine. If not, then re-create the index after saving to make sure it's in effect.Best,
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