@Sala thanks. I’ve checked the headers and again and I can’t see anything in the specific code I provided that would cause the bbcode to not display.
Does it work if you remove all the headers? If this is the case, my recommendation would be to enable them one by one and find out which one actually causes the issue. Once we know which one it is, we can then modify it to allow the display of bbcode.
It just seems odd to me that everything works fine on a new post, but not on reply. This would tell me they it’s not the headers, but I could be wrong. You may want to try disabling wp-rocket to see if that resolves the issue rather than removing the headers.