Hi exedocent,
Are you using Chrome? I am using a Lenovo Yoga with a Wacom pen and this problem drove me absolutely insane for about an hour. What worked for me is going into chrome://flags and disabling Direct Manipulation Stylus (it was on default for me, and all it did was scroll and was very inconsistent in letting me click, which sounds like the same thing you’re dealing with).
I hope this will help you and/or others, good luck!