/execute command doesn't work when paired with /summon

Alright, so one of my favorite things to do in creative mode is messing around with command blocks. I was at a test world messing with the /execute command as always. Today minecraft updated to the newest version. So I tried running an execute command, and it didn't work! That usually happened when there were way too many mobs, so i tried using /kill 2-3 times before trying again. Still didn't work, even though the entity count was down by a lot. I tried a different world, but it wouldn't work there either. Heck, I even tried to use it only 1 mob, and it still didn't work. I tested out that it isn't something with the summon command, so the execute command has to have some bug. I checked the update changelog too on feedback.mincreaft.net to make sure there wasn't some change to the command. Please fix this bug, I would highly appreciate it!