Hello, That's the strange thing, permission issues are correct both in folders 755 and in files 644.
The only strange thing, let's say it like that, is that when I installed an SSL it started to give me that problem, I deleted everything, reinstalled everything, but it stayed with that error, and no matter how many times I deleted the SSL it doesn't even log in securely anymore, I say that I don't know if it's related, in another installation of a panel I've never had this type of problem.