When changing users and groups in applocker policies the mmc crashes. After a lot of investigation a lot of people said that it was a bug and it was fixed in Windows 10.
I identified the following .NET updates;
I uninstalled all the above .NET and I could then edit the applocker rules.
On the 2nd dc i tried to figure out which one of the above updates caused the mmc to crash. I was lucky i started to uninstall KB4024847 and rebooted the machine and everything was working.
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