I don’t know whether this is just a glitch or whether it was intended (it’s impossible to tell with 343…), but after sprinting, when you pull out your gun, there’s about a 1-2 second delay before the reticle pops up and you can shoot. This has killed me many times.
When your sprinting, you’re not aiming at anything, therefore, the reticule is gone. When you stop sprinting, you aim, therefore, your reticule comes back.
What your describing, as said above, is totally normal and is supposed to happen. I’m experiencing something a little different, though.
I will sprint, get to an enemy, and stop to bring my gun up. My reticle will show up, I’ll start shooting, and then my Spartan will go back into sprinting for a second, re-lowering my gun, and usually getting me killed.
At first I thought it was just me getting to worked up and pushing the stick back down, but it continued to happen even when I made sure I wasn’t pushing the sprint button.