They are tedious. They start late. Everything stops while they fix a problem. Couldn’t they have figured this out ahead of time?
It doesn’t matter. It is what it is. Take a deep breath and be patient. Everyone is frustrated. Stay attentive to what is being said by the director or the technical crew, so you can help them. Don’t get so involved in conversations with other actors that you lose sight of why you’re here. Be as helpful as you can by getting into position when they need you to be somewhere, and by running something as many times as they need to to get it right.
You’ve had a lot of rehearsals to get it right. The crew gets one, and there are all kinds of other reasons you aren’t privy to that the Tech isn’t going smoothly. Don’t roll your eyes or lose your temper. It will all be over soon. And don’t worry that you can’t do any decent acting at this rehearsal. It’s not for you, it’s for them. You can act in the dress rehearsal.
This doesn’t mean you shouldn’t try your best. No, you may not be able to sink into the character in this rehearsal, but the crew needs to understand the general timing and events of the show so they can match their cues to them. Be sure you give them what they need.