My girlfriend will intentionally late reply. I know the obvious answer would be "it's because she isn't interested" or whatever. I know that it definitely isn't this. Equally, it's not that she is "busy", so don't suggest this is the reason. I know it isn't, as I explain below:

This is going to sound petty, so to test whether it's intentional, I have on a few occasions sent her an image saying something like "have you seen this? Crazy!", just to grab her attention. She'll really quickly pop up as "online" on WhatsApp, but she turns off "read-receipts", then reads my message and then goes offline. Sometimes she'll forget to turn back on "read-receipts" and then reply, so when I read her message it still shows mine wasn't read. It's getting really pathetic. It's starting to annoy me. I feel disrespected.

I refuse to play along the games, so when she messages I'll typically respond within 1-2 minutes if I'm not busy. Despite me replying within a couple minutes, she'll still reply late.

What can I do to solve this issue? Please, do not try suggest things like "she's busy". Please offer advice based on the assumption that she is in fact intentionally replying late, and reading my messages, but then not replying for another hour. I know you may think I am jumping to conclusion, but I know it's the case, so please don't doubt my judgement. I just want advice on what to do given what I strongly believe is the case.

I am trying to logically understand why a girl who loves me, and is otherwise a good girlfriend, would deliberately delay her replies? I think the only possible reason could be that she doesn't want to come off too "keen", "eager", or like she hasn't got anything going on in her life. But this honestly just makes me actively dislike messaging her, knowing she does read my messages, but chooses to reply late.