The exhibits are well suited bu some of the animals still aren't happy...

If the exhibit is intact - Check the animals themselves. If animals are hungry, sick, lonely/too crowded or the exhibit is too dirty, the animals will be unhappy. If these factors are not a problem, check to see if they're feeling crowded by people. Some animals are shy and do not like to be viewed all around, so try closing off the exhibit except for a few areas; if this doesn't work, what I do is build a fully enclosed exhibit with their main needs until they settle down then place them back in the fully built exhibit but keep it closed. Eventually the animal will be happy and comfortable to have it opened up 3 - 4 spaces again. Some animals, however, just get angry easily and are difficult to keep happy. Just sell them (If possible) and get new ones in the exhibit. Some animals crave enrichment like swinging logs or climbing trees/bars/rocks to be happy in their exhibit. You can fund them in the Research/Conservation tab to make them comfortable.