I have created a dev subdomain on the same server and created a copy of my website for testing. Everything was fine for 5 minutes after it looks like not load properly (see the picture attached). Please could advise what could happened.
I hope you also copied your database and changed the config files so you are using another database?
Yes, all changed and what I am saying for first 5 minutes was ok. Database is copy of original. I think after I have cleared a cache and happened. Same happened to me on localhost, but I thought is maybe wrong setup of php or other settings. But now on the same server...:(