If they are on site why not interview them? If the purpose of these online assessments is to be the mouth of the funnel that process is starting to fail.

https://www.reddit.com/r/leetcode/comments/1mu3qjt/breaking_...

There are funded companies set up just to help you get past this stuff.

https://www.reddit.com/r/leetcode/comments/1iz6xcy/cheating_...

Personally I feel software development has become more or less like assembly line work. If I was starting out today I would seriously consider other options.