Summary:
Console logs from a job which generates a big, long, single line of output don't wrap in the Blue Ocean UI, but they do wrap in Classic.

Steps to recreate:
1. I've used the following Jenkinsfile. Mine is in a multibranch project, but you could probably use it in an inline job:

pipeline {

    agent any

    options {
        buildDiscarder(logRotator(numToKeepStr: '20')) 
    }

    stages {
        stage ('Make a huge long string') {  // start of parallel wrapper
            steps {
                sh 'for i in `seq 1 100`; do cat /dev/urandom | env LC_CTYPE=c tr -dc \\\'[:alpha:]\\\' | head -c 50000; done'
            }
        }
    }

    post {
        always {
            echo "ALWAYS --> Runs all the time."
            // Delete our work directory to save on disk space.
            deleteDir()
        }
        success {
            echo "SUCCESS --> Whatever we did, it worked. Yay!"
        }
        failure {
            echo "FAILURE --> Failed. Womp womp."
        }
    }

 }

2. Run this job, and look at the log output in Blue Ocean. It's not obvious at first glance, but there's a small horizontal scrollbar shown:

3. If you use the scrollbar, you'll end up with a large, blank white area:

4. This might not come out in a screenshot, but I'll give it a try. The super long log is actually visible...barely! It's just a trace amount darker than its white surrounding. I actually thought there was some dirt or something on my display, like from my keyboard:

5. Turns out, this is actually selectable and clickable. Here I've highlighted a small part of it:

6. And here I've double-clicked one of the two lines:

7. I realize this is kind of a nutball Jenkinsfile. It was originally created for performance testing - and it's really good for that. So, I bumped down the character count to a more reasonable 300:

8. For comparison purposes, here's the 300-character version as shown by Classic.

This issue seems pretty similar to JENKINS-35719.