Incomprehensible site redirect?

Question

Domain name market

Good afternoon dear community.
I would like to know your opinion on this issue:
There was a site (self-written), the customer demanded to transfer it to another domain .. transferred (after checking the database and content for the presence of "old" links, correcting the configs and clearing the cache). the domain is displayed and works perfectly, I also checked it with colleagues, and the customer redirects to the old domain from a computer, it works fine from a tablet and mobile phone. htaccess looked, nothing strange found.
Thanks for any advice and your time.

Answer 1

Did the customer try to clear the cache corny?