Yes, that’s what are in my (Richmond California) Planet Fitness. I won’t be able to check on the machines again until the pandemic has passed.
My test was simple, I brought in a bathroom scale and compared my weight to my weight plus the bar in various positions. The bar moves easily, it’s not stuck or anything.
When I told the staff about my findings, they were like, “Oh, ok, weird. Cool. Thanks.” :-)

Very strange! I believe Planet Fitness uses Hammer Strength Smith Machines like this one, right?
https://lifefitness.com/facility/products/hammer-strength-benches-and-racks/smith-machine

All 4 power racks at my Planet Fitness have this variable weight thing going on. All are about the same… 10->20 lbs, 13->24 lbs or so. They are working smoothly. It’s just a thing!

I wonder if there’s some friction going on with either the carriage or the counterbalance? I don’t think they would intend this as a feature.

I can imagine some reasons why they reasoned that was a good idea: easier on the back at the start, less crashing at the top, smoother feel… It makes keeping track of my workout a little weird. I’ll just call it a 20 lb bar, I guess!