Permalink manager

Unfortunately, that does not really tell me much. Could you explain what is going on in more detail, so I can try to figure it out?

Could you possibly record a video showing what exactly happens when you try to update the custom permalink? Is it possible to change it using “Tools -> Permalink Manager -> URI Editor” section?

Thanks, now I see it. Could you check if it is possible to change the custom permalink using “Tools -> Permalink Manager -> URI Editor -> Posts” section?

If so, the problem is probably in JS function, could you check if any JS error or warning is displayed in browser’s console log?
https://developer.wordpress.org/advanced-administration/debug/debug-javascript/#step-3-diagnosis

Ok, is it possible to change the custom permalink for this specific post using “Tools -> Permalink Manager -> URI Editor -> Posts” section?

If it is not possible to save new custom permalinks, the problem is probably either in the size of the custom permalinks array. Send me two screenshots:

1. One with the size of custom permalinks array (you can find it in “Tools -> Permalink Manager -> Debug”)
2. One with “max_allowed_packet” and “PHP Memory Limit” values (you can find them under “Tools -> Site Health -> Info”):

There is a chance that there might be some PHP warnings or errors listed in PHP error log. Have you already checked them? If not, you can try to use this mini tool to log them (if there are any):

https://wordpress.org/plugins/debug-log-manager/