Imbuing Towers don't grant Onslaught despite anointment

I have anointed one of my rings with 'Your Imbuing Towers also grant Onslaught'. Despite standing in the radius of an Imbuing Tower, Onslaught is not granted. At least, the buff icon for Onslaught is not shown (see picture below).

https://imgur.com/a/XRTRtzg