The attack mechanic is set up in a way so that only right-clicking an enemy while your power gauge is not at 0 allows you to attack.
This means right-clicking outside of an enemy does nothing, and right-clicking an enemy with power at 0 does nothing. The former was an intentional design choice to force people to have to manage the number of anomalies missed because otherwise you could deplete your gauge to a safe amount (~3) at the end of each round and that dampens the management aspect quite a bit.
Enemies do move fast, and there is a tiny bit of delay to the attack in order to sync up with the clap animation, so try to aim with the delay in mind. You can exploit the delay to deplete your gauge faster by spam-clicking if you want (this is intentional). I hope this information helps.