Safari: Safari A problem repeatedly occurred

My MacBook Pro 10.13.6 running Safari version 13.1 started having problems loading web pages last week.

As a webpage is loading, the following message appears and the webpage starts reloading:

This webpage was reloaded because a problem occurred.

After that happens a few times, a gray screen appears with the following text:

A problem repeatedly occurred with <URL>

There are older questions about this problem, but I haven't seen a proper solution on those.

There are no extensions loaded. The cache is cleared. I am using Norton AV. The problem doesn't occur on some websites, while others are no longer usable at all.

Help is appreciated!