Could it be the transmission fluid?

My car has delayed engagement with it’s automatic transmission after putting it into drive. It feels like the clutch is not engaging right away (usually a couple seconds). It doesn’t always do this. It does it intermittently, I think more when the engine isn’t warm. The mechanic said it was likely not anything to do with fluid because if it was, it wouldn’t be intermittent, it would be all the time. Is that true or could it still be a fluid issue? Everything I’ve read suggests potential fluid level problems. Thanks in advance.