Is it normal for my car to pick up a rear wheel in hard corners?

Wheel lift on three tires in a sweeper means that corner is genuinely unloaded, so yeah, you are losing grip there at that moment. It feels fine from the seat because the loaded tires are doing all the work anyway and the car doesn't snap or wiggle, it just rolls through on a tripod. That's why it looks way worse than it drives. The photo is dramatic, the loss of traction is usally small unless you're hearing wheel spin or feeling the rear step wide.

Same thing happened to me a couple seasons back and what actually settled it for me was a cheap suction-mount camera aimed at the rear wheel. Watching the footage let me tie the lift to specific inputs instead of guessing from the seat, and I noticed it only came up when I was trail braking too deep. Loosened my entry a touch and it mostly stopped. If your times are allready fine I'd film a few runs before touching springs or bars, chasing a stiffness change to fix a driving habit is a rabbit hole.

If the lift only shows up in the tightest sweepers and your lap times are holding, I'd leave it alone for now. I ran a big front bar on my own car for two full seasons before adding any rear stiffness, and the tripod look never cost me anything measurable. The one thing I'd check before chasing springs is tire pressure on that inside rear. I dropped mine 2 psi from my starting pressure and the lift actually got worse, wich told me the roll was doing the unloading, not the air. Small stuff like that tells you more than any guess from behind the wheel.

Interesting reading this because my car does the total reverse of yours, it rolls around a bunch on soft springs and never picks a wheel up, and I always wondered if I'm leaving time on the table by not stiffening it. So is lifting the inside rear mostly a symptom of a front bar doing too much work back there, or can it happen even on a balanced setup if the sweepers are just tight enough? Genuinely asking since I have no baseline for this stuff yet, still figuring out what my car is telling me.