Using the New Outlook for Mac for personal email and calendar
I have the same issue and looking around the web and this forum so do plenty of others. The fix is to set BOTH the MaximumConflictInstancesAllowed and ConflictPercentageAllowed parameters on the meeting room. If you log into Outlook using the resource account then I believe you can set both through the UI, but you can also do it with ExchangePowershell:
Install-Module ExchangeOnlineManagement
Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline
Set-CalendarProcessing -Identity ******@contoso.com -ConflictPercentageAllowed 50 -MaximumConflictInstancesAllowed 100
In the above I'm allowing ******@contoso.com to accept recurring meetings as long as no more than 100 instances AND no more than 50% of the instances have conflicts. The higher you make each of those values the more forgiving the room resource is. There's a really good presentation of this here.
Note that if you don't want the meeting room to create conflicting bookings then make sure -AllowConflicts is set to $false (which I found very counter intuitive at first, but the blog post I reference above has a really good flow chart that explains the interaction of these three parameters nicely.
Hope this helps!