It is under normal usage that I detected the issue on mine pal. It's an issue because it's a gradual increase in the height difference from the right to the left of the bottom where speaker grill & the screen mean. This gradual increase in height makes me think it's the uneven application of the glue for the speaker grill or some dodgy clamping whilst the two surface mate that's the cause of the issue.
And yes, it gets annoying as your thumb slides over it again & again.
I know you can feel a slight join, but that's because there is a join. The One is unusual in this regard as it's not a slab of glass like most other phones.