The Archdiocese of Los Angeles sued to block the sale in 2015, arguing the nuns did not have authority to sell the property to Hollister.
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So the dispute is really between the archdiocese and the nuns.
IIRC the nuns, or perhaps sadly now, the nun, claim their order’s property wasn’t under control of the archdiocese but rather directly under the Vatican. So the archdiocese had no authority to botox the sale. Which is conceivable, but I haven’t seen whether the Vatican had weighed in on that claim.