It suddenly occurred to me that this bug could have also been caused by the new copy alert work.
I did some additional testing to see if I could pinpoint the cause of the problem. After reverting the code that was added for the holds pickup work on bug 1661688, I found that the "Item On Hold Shelf" alert only displayed when checking out to somebody who is not the holds patron, as is the expected behavior.
It suddenly occurred to me that this bug could have also been caused by the new copy alert work.
I did some additional testing to see if I could pinpoint the cause of the problem. After reverting the code that was added for the holds pickup work on bug 1661688, I found that the "Item On Hold Shelf" alert only displayed when checking out to somebody who is not the holds patron, as is the expected behavior.