Failed to connect and Checkpoint offline

I started playing the MCC last Monday, and I will admit, I have run into a few things that made me scratch my head. However, today seems to be the worse for me. After my first match today of matchmaking, I keep getting the failed to connect message. Nothing has changed on my end for the set up but I don’t know why it keeps telling me this. So, I thought I would continue playing the campaign. (At halo 2 and love the anniversary treatment) Sadly, I found problems here as well. And before you ask, iron skull was not on. I tried playing through the level where you get to ride on the scarab and was going to jump on it but I failed my jump. I laughed a bit when it happen because I find it funny because of my fails. However, my laugh turned into a “Wait, what?” as I was now at the back the beginning. Confused I backed out to see if I had put iron on but it wasn’t. I tried resume my save for halo ce’s the maw, where you where at the warthog run and found it lost the checkpoint. So, I continued through of the level and until a was attacked by flood with rockets. (I don’t like him.) I thought I would load up to the checkpoint that I say appear before I went to the cryo room but once again, I was met with the opening cutscene. (Still, no iron skull on) I would just like to know what is going on because I haven’t had any major problems with MCC. I hope someone can help me and thank you for reading this through.