iMessage saying delivered on one device but not on the other
My sister just got her first iPhone after graduation from university, and whenever I send her a message, it is really odd. I sent her the first two messages congratulating her for getting an iPhone and for graduating from university from my MacBook and it said 'delivered' on my MacBook Pro 16" m1 immediately after sending the message. But three minutes later, I sent another message to her but this time, it does not say delivered on my MacBook Pro. However, the same message does say 'delivered' on the iPhone 14 Pro Max. Then, I sent her a message on my iPhone 14 Pro Max. Again, it does not say 'delivered' on the iPhone 14 Pro Max, but it said 'delivered' on my MacBook Pro.
That meant any message I sent from my iPhone would not say 'delivered' on my iPhone but it would on my MacBook.
And any message I sent on my MacBook would not say 'delivered' on my MacBook Pro but it would on my iPhone.
I texted her on my 16:9 app testing phone on a different iCloud account (iPhone SE 3) days prior and some of the messages only say delivered several hours later (I sent one message at 3:06, it does not deliver until around 10:00 and another message at 10:40 does not say delivered until sometime around 14:30, which is kind of odd, given my iPhone is connected to WiFi and is not on a cellular network
I am scared my sister might have already blocked me if the iMessage system is so inconsistent like that.
iPhone 14 Pro Max