It's probably the kava that you're drinking. I had a few kavas like that: little actual impact on anxiety, lots of side effects, which means I drink more to relieve anxiety, get more side effects, etc. One tudei I drank I wouldn't feel anything except for the hangover the next day.
Sometimes I don't get enough sleep, or my mood/stress is already bad when drinking kava, so the session might not be as optimal. Still, with Papa Ele Ele I've been getting consistent results with the same dose every single night. I need to meditate, exercise, eat well, socialize, or play video games once in a while too -- kava needs stress reduction allies.