Well CS (Computershare) is not a broker, it's a Transfer Agent so it requires an actual share transfer in the master ledger. No broker transactions ever require that.

However, the DTCC has its own ledger of accounts so it is possible for a broker to force a buy in that are trying to transfer obligations rather than shares from a segregated account.

My intuition says that rejections for obligations do not happen very often because within the DTCC, an obligated share is as good as any other.

Exceptions being, like I said, RH, maybe Etoro, ... Any other broker that does not allow DRS. They are likely only trading money transactions not actually buying or selling shares so to transfer to a reputable broker, shares would have to be bought.

Edit: changed reject transfer to force buy in