>> delayed receipts
Can also depend if the recipient has had their phone switched off or network unavailable at the time the text was sent.
Dad turns his mobile off each night, and Ive repeatedly noticed that when he switches it back on again, it can take a while before any texts that were sent during the time his phone was off, actually get sent to him.
Its almost like because they weren't able to be sent immediately, then theyre held somewhere which only tries every so often to resend.