Why does another site open while my domain is written in the url?

Question

MODX

I have two sites (site1.com and site2.com) located on the same vds under the same ip. I use Plesk as a dashboard.

At some point, sales on site1.com fell and on the computer of one of the buyers, I saw that when site1.com was opened, site2.com was displayed. There is no redirect, site1.com remains in the url.
I'm using the Plesk panel.

I'm trying to find the reason. I have no idea what could be the issue. Maybe a glitch from plesk?!