In the following article, (https://support.oneidentity.com/active-roles/kb/239069) you can see a scenario where your dynamic groups may not automatically update without a rebuild being performed. However, if you have many, or all of your dynamic groups that meet this criteria, your dynamic groups may not be so dynamic anymore. The following script can be used to rebuild all dynamic groups as there doesn't appear to be a way to trigger the rebuild directly on a group.
# Builds controls to bypass Dynamic Group Policy to allow clearing of group members
$hash = @{}
$hash.add("EDS_CONTROL_FIX",4)
$hash.add("EDS_CONTROL_CHECK_POLICY_COMPLIANCE",5)
$hash.add("DGPolicyGUID","84C1A76B-2A6B-4f4b-837A-22D2CCAC777A")
# Loop through the dynamic groups and remove all their members
Get-QADGroup -Dynamic $true -Proxy | ForEach-Object{Remove-QADGroupMember $_ -Member (Get-QADGroupMember $_) -Control $hash}
Also note that the above can be used on a single dynamic group by modifying the Get-QADGroup cmdlet to only return the single group.