My T says it's not only normal, it can be a good thing too. And as Elio explained very nicely, people with certain kinds of issues or trauma will have more problems with dealing with the conflicts that come up. I think differences in relationship are normal, having trouble handling it is something to work on.

I'd differentiate of course, if it's every session and it doesn't get worked through, you'd probably need a second T just to process all the ruptures from the first one... that's not normal or good.
Having them from time to time, sometimes more sometimes less, is pretty standard I think. It's not any different from other close relationships. I fight with my partner, my friends, my parents, my grandparents, sometimes even my closer neighbors. There's people I constantly only fight with and those I don't usually try to interact with. But there will always be moments where for whatever reason, we are bothered by the other person's actions or what they say and react to that. This is true for almost everyone.

I by now am pretty convinced it actually can be a good thing, especially in therapy. If your T, like L sounds she does, reacts properly and you can learn from the experience, over time the reaction should get less, also leading to more understanding. Actually, just yesterday I had an example of this with my T in session:
I remember once my T said something - no idea what anymore - that bothered me. I got really, really dysregulated, cryed, probably my tone of voice changed a lot too, though I still remained respectful and everything. I was still able to talk to him, but I certainly wasn't in the mood to cooperate or understand what's going on.

Yesterday, my T was quiet for most of the first 10 or so minutes of my session, although I brought up various topics that I would have liked to breach and I think there might have been some good stuff in there. I, finally, came to my last option for topics, which was more about the past than present, but I didn't feel like talking about it too much, it really was a last option. He reacted a bit to that, but at some point we both got quiet again. If that goes on for too long he usually asks what I'm thinking about, so I just waited until he did that and then told him I was bothered by how he wasn't talking. We talked about it for like a minute or two, but I wasn't really THAT mad, I was a bit irritated moreso. And then we were able to talk through why maybe I was bothered that at some points he talks less and more just listens, if he's still there and pays attention.

Through the repeated ruptures by now I've kind of learned that they do happen from time to time, but they don't destroy the whole relationship. And through that I can also regulate myself more and we can talk about deeper connections in a way that it sticks more, so that hopefully some day I'll also be able to do the same thing outside of therapy.