Haven't tested it out this patch but animal companions were not leveling up at all.
It took a bit of googling but I did find this:
"Well, WotC released a clarification on how it works now, but in essence it has the stats of the animal you are getting ( However, if it would get multi-attack, it loses it for balance reasons ), but it has the same proficiency bonus as you. It gets the proficiency on it’s AC and on its damage rolls. It get’s proficiency on two skills of your choice, proficiency on all saving throws, another hit dice whenever you level up, when you get a ability score improvement, you also get it. It shares your Favoured Enemy Feature."
https://www.quora.com/How-do-animal-companions-work-in-D-D-5e