My girlfriend just goes off the grid for hours now, what does it mean?

My girlfriend and I have been together for 5 months now. Normally when she gets busy with family stuff she tells me. Which is perfectly fine. Recently she's just gone off the grid for hours and giving reasoning such as "I went here and home and back out and home then here then there"
most recently she went off the grid for 8 or so hours. Our relationship difinitely isn't what it used to be. We don't talk as much anymore and now this

Do I need to be worried?
My girlfriend just goes off the grid for hours now, what does it mean?
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