Steps to reproduce:
1. Add this script to project with Entities installed:

using Unity.Entities;

public class NewBehaviourScript : SystemBase
{
private float timer = 3;

protected override void OnCreate()
{
Entities.ForEach((Entity e, int entityQueryIndex) =>
{
timer = 50;
}).Schedule();
}

protected override void OnUpdate()
{
throw new System.NotImplementedException();
}
}

2. You'll get the error in console:
"error DCICE001: Entities.ForEach Lambda expression uses something from its outer class. This is not supported. Seeing this error indicates a bug in the dots compiler. We'd appreciate a bug report (About->Report a Bug...). Thnx! <3"

Expected: No errors, or compiler not allowing that code to pass
Actual: Error told me to send a report, so I did.

This was reproduced on Entities Package version 0.6.0, 0.9.1; 0.11.1-preview4
(Can't be reproed with same code earlier than 0.6.0)
Unity version 2019.4.1f1 (e6c045e14e4e), 2020.1.0b4, 2020.1.0b12