The type of the resource mailbox can't be blank. It should be either Room or Equipment.

LeonPavesic 

Thanks for detailled reply, unfortunately all those things were already tried.

The types are already good as said in my post.

Online command:

Set-Mailbox -Identity "HoChiMinhViettelTower_MeetingRoom01" -Type Room
WARNING: Couldn't convert the mailbox because the mailbox "HoChiMinhViettelTower_MeetingRoom01" is already of the type "Room".

OnPremises command throw the error as indicated also in my original post.

The mailbox work properly, so repair commands Online are not going to fix an error on the OnPremises command.

Active Directory Attributes are filled properly:

Get-ADUserByUPN -UserPrincipalName email address removed for privacy reasons -Properties * | FL *recip*

msExchRecipientDisplayType : -2147481850
msExchRecipientTypeDetails : 8589934592
msExchRemoteRecipientType : 36

Example of another room that does not have the error:

Get-ADUserByUPN -UserPrincipalName email address removed for privacy reasons -Properties * | FL *recip*

msExchRecipientDisplayType : -2147481850
msExchRecipientTypeDetails : 8589934592
msExchRemoteRecipientType : 36

Again I compared all properties with a room without this error / warning, and everything match.

Yes last time it happened, disabling and re-enabling did the trick, but this is not a satisfying solution. Microsoft should find the source of the error and allow us to run a fix.

How do we report this kind of bug officially so Microsoft finds a fix?