Usually this is because of LS Mirrors of VSROOT. When you create the volume, the namespace mirrors are not updated until the schedule updates... check snapmirror and confirm then add a step to snapmirror update-ls-set after any namespace changes. It is likely working after 20-30minutes since you probably have a 30 minute or sooner schedule for those mirrors. When LS Mirrors are present (best practice to protect the vserver root) then the mirrors don't have the new volume junction path until the update is done.
Another note is that system manager will show ls mirrors and will even allow you to run the update button, but it won't update (and doesn't give an error unless you check event logs). Only from the cli with snapmirror update or snapmirror update-ls-set.
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