During the last fight, Bianca's hair changes. She has her in two braids, in some shots the braids are all one color in others you can see colored highlights in the braids.
In the training sequence in the desert, at one point Creed's knuckles are all bloody from training. The next day in multiple scenes including falling on the road, sitting on the water tank, and being on the phone, his hands are perfectly fine.
The sonogram for Adonis's daughter says "Creed," and Rocky and Adonis later discuss "Kate Creed" as a possible name. In "Creed," Adonis's last name is Johnson; he only uses Creed as a fight name.
When Adonis goes down in the tenth and final round, he repeatedly punches the canvas and then gets up to eventually win the fight. However Adonis was down for way more than ten seconds. Viktor Drago should have won the fight by knockout. The same can be said for the two times Viktor is knocked down. Both times he was down for at least twenty seconds before he got up.
When Adonis holds his father's belt, the South African flag is shown as it it today (incorporated in 1994) - well after Apollo won the belt.
When Viktor runs in front of his father's Land Cruiser in Ukraine, it's clear judging from the scenery and architecture of the buildings around that the scene was filmed in North America.
During Adonis' first fight against Viktor Drago, one of the sportscasters calls Viktor by his father's name "Ivan Drago". Yet the subtitles say "Viktor Drago."
Prior to his fight with Danny "Stuntman" Wheeler, the Tale of the Tape shown on-screen states Adonis's age as 28. This is impossible. Adonis was born between 1985 and 1986, making him at least 31-32 by the year 2018.
During final championship fight with the American Creed fighting the Russian Drago in Russia, Drago is knocked down during one scene and the referee who is supposed to be Russian can be heard counting in "English" then in another scene where Drago is knocked down the referee can be heard counting in "Russian".
In multiple scenes, B is seen without the earpieces in both ears. Especially in the final fight.