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the web site have a very slow response and when i open error log i can see
---OSError: write error
---NumExpr defaulting to 4 threads
what seems to be causing this issue. the website was working great before even with these errors apearing.

The "write error" is likely a symptom of a problem rather than a cause -- if your site is running slowly, then browsers will disconnect before you can return a response (eg. if the user decides to close their browser tab because a page is taking a long time to render), and then there will be a write error when the system tries to write a response to that closed connection.

Regarding the slowness in general, this help page has hints and tips on how to dig down into the causes of performance problems.