My girlfriends Instagram activity is really concerning me?

So I (32) and my girlfriend (30) are just beginning a LDR relationship due to unforseen circumstances. We have been together for 5 years and due to jobs we will be apart for a few months. We have been managing things well and we talk every day. However... Her instagram activity is bothering me. Most nights now after we send a few late texts I often don't get a reply till the next morning. I send a message and then I see her online on Instagram till 2 or 3 am. I have not said anything about this but the odd night I have sent her another message asking if she is still awake and she does respond, saying that she is reading. I just find it a little but strange that she stays active on the app and yet may have a message from me that I am waiting on a reply to? She does not be active on WhatsApp though that late and if she does go online she will reply.

My girlfriends Instagram activity is really concerning me?
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