8 month old gags then vomits food

I'm new to the group so I do not know if this has been asked before. My 8
month old boy is bottle fed and eats beginner/6month old baby food. We
tried him on 8 month old baby food a couple of times and he gags then vomits
everything he ate in the past few hours. We stopped giving that food but
every now and then he does the same with the cereals that we give him and
they are relatively smooth. He has been eating cereal for some time now so
I don't know why he gags on it now.

Any ideas on what might be going on?

Thanks