Amethyst doesn't recognise the uppercase N in the second npub. I always put an @ in front an npub although I'm not sure clients still require that.

Npubs

MirbooHodl: nostr:npub1jeyv5qwg4286fm68vwj93yr53xv9g799w9vcz8al8mkkz36wkt4qektpt7

88 Sats: nostr:npub1ke3gzakud8hvdpmxxkhzymf87tkznnhmlj78gdqj4t9rqqmkhlws52gfzw