Sunil,

I found this and thought it might be useful:

"The number of requests allowed in the default (UI) semaphore pool is 16 processing (number of semaphores) and 150 in the queue. After the queue maximum is reached, the system will not allow any more."

I found this here: https://hi.service-now.com/kb_view.do?sysparm_article=KB0594813

Hope this helps you or someone else. It helped me.

Kenny