Texting my guy friend/crush – why does he respond like this?

I (F) am talking to a guy friend/crush through text and he sometimes has the habit of weird response times. Meaning, we will be talking back and forth (a flowing conversation with relatively short reply times) then eventually he will just stop replying completely (mid-conversation). But he has his read receipts on and it shows that he read my last message but will take him like a day to respond back. Is this a red flag or concern???

I know people can get busy or distracted and texting is not the most direct way of communicating with someone. But I just find it weird that he would up and “leave” the conversation for hours at a time, despite just talking back and forth.

Note: it doesn’t happen all the time, but it has happened a couple of times and was confused about what it signified.

tl;dr Why would a guy text you back quickly numerous times then take a day to respond to a message despite having read it?