I'm having an issue where the Pulumi diff shows a resource to be replaced (114 unchanged, 1 to replace) , but when pulumi does the update, it doesn't replace the resource, just says 115 unchanged.

That is fairly common. It happens when Pulumi cannot know the value during the dry run (preview / 1st part of up), and reports the potential update. Then when the update actually happens, there is no change (old value = new value). Common culprits are values that get pushed to vaults or secrets, but there are other cases too.

Hmm. Thanks.