Can a person receive a message that wasn't even delivered?

Are you confused over the Whatsapp messenger timestamps? Know from our experts when the timestamps in Whatsapp messenger message differ for senders and receivers.

I was chatting with my girlfriend on WhatsApp. It was about 1:40. She suddenly left without saying a word. I waited for her to come back for about 2 hours, but she didn't. I sent 2 more messages. At 2:40 and 3:40.

Later, at 10:00 I opened the chat. Both messages had 1 tick. They were sent, but not delivered yet. She then replied at 12:06, and said she had received both messages at 4:00. However, the message information says they were delivered (2 ticks) only at 12:04 and 12:05 respectively. We live close, so the time zone is the same.

Is this a common WhatsApp server issue? Could bad Internet Connectivity be the cause?