Stuff not existing

Been working on a map for a bit. I've been able to summon in and use Barriers in the past, but now it doesn't seem to be working. Also where I had them placed before have disappeared as well. So I went and did a little test to see if anything past the barrier update worked. I tried to summon in an Endermite and those don't exist either.
I've tired summoning both through the chat and command blocks. None of the options work as if they don't exist in the first place.