some request is not sent inside the random controller

### Expected behavior

Random open google, bing or baidu in 20 loops. google, bing, or baidu are opened randomly, and the total request amount is 20.

### Actual behavior

bing is opened only once. The total request amount is less than 20.

### Steps to reproduce the problem

1. Create a new thread group, and set [Loop Count] to 20

2. Add a [Random Controller] into the created Thread Group
3. Create 3 [HTTP Request] to open bing, google and baidu

4. Start the script

### JMeter Version

5.5

### Java Version

tested on java version "1.8.0_301" and openjdk version "11.0.2" 2019-01-15

### OS Version

MAC 13.0.1 (22A400)