What is a strange PHP issue? As a result, all websites cannot be opened,

A strange PHP problem found? All websites cannot be opened. ask for help! The vps I use is a linux system that uses the lnmp one-key installation package to build an environment. I recently installed a wordpress theme, and modified some code of the theme. it didn't have any problems after it was changed. later, I found that the website could not be opened in a few minutes, A few times I couldn't open it, and I didn't prompt an error. Google browser prompts 101 error. Why did you find a strange PHP problem? All websites cannot be opened. ask for help!
The vps I use is a linux system that uses the lnmp one-key installation package to build an environment.

I recently installed a wordpress theme, and modified some code of the theme. it didn't have any problems after it was changed. later, I found that the website could not be opened in a few minutes, I couldn't open it after a few clicks, and I didn't prompt any errors. Google Chrome prompts 101 errors or something, but refreshing the error prompt is different. Use a third-party tool to check whether the http status code is 200 or 302. In short, the website can be opened at a time and cannot be opened at a time. the two cases are in the tens of seconds and there is no regularity. then, other websites under the same server are opened and the same problem is found, this is strange. if the wordpress code cannot be opened because of an error in the previous modification, it is also a problem with the website. how can it be involved together with other websites? Different directories and different programs.

I tried to restart nginx, PHP, and VPS.

I don't know what I mean. website A is A wordpress program. I modified the theme code before this problem occurs, but there was no problem after running for several hours, in the evening, I found the problem. A is under the/home/www/A directory, B is under the/home/www/B directory, and website A cannot open website B, A can open B.

Another point is that I ran to the theme author's homepage and found that his website could not be opened.

Is this weird? What's the problem? Thank you!

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I think there are still many imperfections in php. for example, when I use the ISAPI (php version: 5.2.17), If I submit a file again after several minutes or longer during the POST upload process, the WEB server will crash randomly. PHP bugs and stability need to be improved.