It’s frequent enough to be annoying.
One scenario is two factor involving SMS messages - once registered to a service, only the registrant seems to be able to de-register it, thus making it impossible for a new number owner to register it.
Another is who owned the number before you and dumped it - and now all their debt collectors are calling you trying to get money from them.
Experienced both after moving country and getting “new” numbers. And having to spend $5 each time I changed numbers to get around the sms thing.