The current system unfortunatelly requires that the Swim PR are supported by the device, hence although the information is available in your account, it won't be displayed on the PR table, and it won't change unless Garmin decides to rewrite the feature so, that it stops relying on the device for this purpose.
More about Pool Swimming PR, incl. the list of supported devices can be found here: https://support.garmin.com/en-IE/?faq=O8rHgFa3iB2HpErPIxL4v5 (Instinct unfortunatelly not being on that list)