Permissions issue with RADIUS authentication on HPE 1920-24G-PoE switch

I've set up an HPE 1920-24G-PoE switch (JG926A) to authenticate against a Windows NPS server. Authentication is working fine, but authenticated users do not have manager permissions. I've set up a vendor-specific attribute as follows:

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Vendor Code: 25506

Vendor-assigned attribute number: 29

Attribute format: Decimal

Attribute value: 3

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Essentially the same NPS policy (aside from this vendor-specific attribute) works perfectly on my Procurve 26XX switches with aaa authentication login privilege-mode set.

Any ideas what's going on?