Errors when loading files in html (,, ). Whose cant? Mine or the server?

Question

Server equipment

Hello to all masters ! There is a site under development. The first week after paying for the server, everything was fine, the code was displayed correctly and without errors. Today I filled in new improvements, threw the battleship to the customer - he is horrified.
The essence of the problem . When loading script files, styles and pictures, some give an error 500, and randomly: it refreshes the page and each time different files, less often it loads everything as it should.
What is the problem, with whom to fight?

Answer 1

If everything worked before loading the improvements, then most likely it is in them.
You need to look at the hosting logs.

Answer 2

T9, as always, let me down.
battleship to the customer > link to the customer
refreshes the page > refresh the page