I have the same issue, mine gets to 22 on a very good day, most of the time it's at 15/16 and as low as 7c at night WITH THE LIGHTS ON ππ
My plants do see to have suffered a little bit when compared to others but over all they seem alright :)
You may want to lower RH to achieve optimal VPD but at this stage of growth its OK. You will need a very arid environment (at 20C) later though. ie Flowering at 20C needs 25-40% RH