Default Limit background app process

Hi guys
I have aproblem when setting the limit background apps process in developer options
At "4 " then i go and launch 4 apps in background..and then when open the task manager i find the phone has killed all running apps
I tried then to restart my phone...and after restarting it i go to developers options, i found the limit has backed to standerd limit choice
I tried this many times..i faced the same thing..
Any one know what is the problem ?!??
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