Front brake lever "sticking" -- weird lever behavior

[AC_Schnitzel]

Here are the details:
- 2009 XB12Scg
- 16k miles
- Less than 2 months of ownership (for me)
- Stock brake lever
- ZTL2 brakes

This started happening recently. Prior to this, the front brake operated normally -- as in, the amount of force required to squeeze the lever was linear (and equivalent) to the amount of stopping power the brake applied.

The Issue
- When slowing down from a speed above 30mph, I squeeze the lever and it sticks to a point and provides maybe 20-30% braking power
- I need to squeeze the lever harder to slow more, and with enough force it goes past the "sticking point" and immediately gives me 60-80% power -- causing my front suspension to compress and jerk the bike forward
- There is no in-between when approaching a stop between the 30% and 60% -- just a sharp application of braking power

What I've tried
- I brought the bike in to a local shop and they inspected the lever, and bled the brake line w/ new fluid
- Haven't tried much else besides that

Potential Solutions?

Based on reading other threads it seems like my solutions could be:
- Glazed/damaged/dirty rotor
- Master cylinder seals are dirty, needs to be rebuilt
- Change fluid and bleed line (which I've already tried)
- Grease lever pivot pin (lever operates fine, not sticky when stationary)

What is the most likely culprit? What should be my next step for diagnosis?

Thanks in advance!