random 502 error on posts

hello,
I have a problem that is amazing !!!

I’ve problems with both old and new posts . I’ve find 5 old posts which display a 502 error bad gateway for no reason and to fix it i’ve to put a url redirection to solve the problem .( the only way i’ve find to fix it)

And also randomly when I published new item, i’ve the same problem. And very strange thing if I edit one and I reduced the number of line , strangely it works . I want to clarify that I have no restriction placed on the number of characters . I did some research on google for ideas , but no one ever had my problem. If anyone has an idea I’m interested. FYI I did not particular plugin installed or updated.

Thank you .