I've noticed this with Lyft recently, and I've been "scammed" by this a few times before I noticed what was going on.
I would open the Uber app, see how much the fare is, then I'd open Lyft and check there as well. Lyft usually is less, so I'd request a Lyft ride.
After hitting the Request A Ride button, a small banner across the bottom appears for a fraction of a second saying "Your fare is now <higher price>" before disappearing. The app then doesn't display the (new) fare I am paying until after I am matched with a driver.
I have contacted Lyft about this, and the response I received basically said that up-front fares are dynamic, and aren't final until I am matched with a driver.
Lyft gets a big
from me. I've always liked Lyft better than Uber due to their customer support, but it looks like Lyft has slid into the same scammy tactics that Uber was known for.