It can be because on your target site, there were both index.html and index.php after the restoration.

By default, WordPress always reads the index.php, and a default WordPress install does not have the index.html file.

The problem is that the target website reads index.html by default, which is the ‘Apache2 Ubuntu Default Page’.

We think your source site should have a rule somewhere that makes index.php take effect instead of index.html, and while on the target site, there is no such rule.

You can try to delete index.html from the target site, and the problem should be gone.