When I click the toggleCollapse button on Queue, it is highly likely to redirect to a page with the path /toggleCollapse?paneId=buildQueue.Page shows Oops! Not Found. This page may not exist, or you may not have permission to see it.
 
My queue length has reached 5,000 and is decreasing rapidly, which might be related to this aspect. 

 
To add, expansion has always been successful, but contraction has a high probability of failure. This issue did not exist in the previous version 2.481 that I used. 

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Supplement of September 9th

I use Jenkins 2.516.3-rc37020.7438172eb_73c, it still occurs.

The groovy script can help you create 6000 long queue. 

The video shows my operation process and task configuration.