Fail to assign "Dial Plan" to Call Queue and Auto Attendant

[nicesiuhung]

Suddenly,  I noticed Dial Plan can't be assigned to resources accounts, Call Queue and Auto Attendant. Might I know what is the common reasons and how to troubleshoot the following issues? 

Dial Plan can't be assigned : 

[#2]

@nicesiuhung Is this on the right track? Errors when trying to manage dial plans - Microsoft Teams | Microsoft Docs