So seems like EA changed the chemistry system up for the WC mode. That was to be expected because it was the case in FUT 14 WC mode also. BUT they changed it now up so that you have no way to get every single player on 10 chemistry each if you're building a hybrid with different confederations. Some will only get 9 chemistry, even with loyalty.
That's because every player gets 8 chem when having the amount of links he needed and gets +2 with a manager from the same confederation but only +1 with loyalty bonus after 10 games.
So in this image Gabriel Jesus is only on 8 chem or 9 chemistry with loyalty. If you're changing to a South American manager, it's the same with Mbappe - 9 chem max with loyalty. So unlike regular FUT there is absolutely no way to get every player on full chemistry even with loyalty when using hybrids.
So Electronic Arts are punishing people for trying to make somewhat creative squads.
Not to mention that you're still only able to make ONE (!) squad in this mode. That was one of the biggest critism in FUT 14 WC mode and yet 4 years later they have not learned anything and are doing the same thing.
Here is an English video explaining the chemistry system in detail:https://youtu.be/Alm-kRTwCq8