For the wizards:

1. One thing you can do is have hidden monsters. Very high stealth rolls or or that was simply out of their field of vision. Perhaps behind them (such as in a hall that was hidden, or on the ceiling, lying in wait) and waiting for the perfect time to strike. 

2. Try making them the main targets. If they provide the most damage or are doing quite a lot to mess with the creatures, make them the main targets. If the creature is in self preservation mode, they would either go for the thing that is hurting them most, what's in front of them, or they would try to run. If they are starving or feel threatened, the same can apply. 

3. You can always make the creatures have a bit of Damage Resistance, magic Resistance, or spell resistance. All creatures can be slightly different. I mean, not all people are the same. So the same should apply to your creatures. 

For the Battlemaster and Cleric: 

1. Sundering armor is an ability that could reduce their AC easily. Or even disarming their weapons. While the Cleric could still have spells, it could make them a bit scared and try new tactics. 

2. You could also simply give them a beefer monster to fight. If the challenge is not there, make it slightly harder. Nothing says you can't make the battle a bit tougher, but be prepared to give them adequate compensation for it. 

These are what I've had to use in my game as well. While the players seemed a bit angry that a certain creature rolled a very high stealth against their perception (Got attacked as the others went into the room silently) and the fighter got his armor destroyed in the next room, they came out of it alive, with new armor, and a newfound respect for how the dungeon worked and operated. They also said that was the most engaging and scary encounter they had had up until that point. 

I hope this helps! Good luck with your games!