I have never heard of anything other than Cloudflare producing a 520. It’s not a standard HTTP status code. My guess is you haven’t successfully removed Cloudflare from the equation. If you really think you have then look for another component in your stack that produces a 520. WordPress won’t. My plugin won’t.
I’ve given you all the advice I have until you can present me with something I can investigate. Please don’t pressure me by saying you’re desperate, or by implying that I’m responsible for delaying your work. I provide a free plugin which you are running on your server, not on mine. If you experience technical issues you can’t solve then I suggest you use a different PO file editor. There are many.
Your screenshot isn’t relevant to the problem you are experiencing.