Lauryn Hill performs with her six-piece band at the Warner Theater. (Josh Sisk/For TWP)

Lauryn Hill has always taught us to expect the unexpected, which means we should sometimes expect her to sound like Frank Zappa.

Her performance at the Warner Theatre on Wednesday night was unpredictable in all the right ways, transforming her sepia-toned R&B into twitchy, aggressive, hard-edged music that resembled vintage progressive rock. It didn’t always satisfy, but it was consistently provocative — as if the quirks that initially made her songs so magnetic had grown monstrous fangs.

Most of the set was culled from Hill’s only solo studio album, her 1998 opus “The Miseducation of Lauryn Hill.” Its 14 songs would help define a ­then-nascent neo-soul movement. It would also cast a 14-year shadow over Hill’s career that she hasn’t escaped. Instead, the 36-year-old singer has spent her 21st century dipping in and out of the spotlight, giving erratic performances that have left audiences stranded between confusion and ecstasy.

But Hill was absolutely present at the Warner on Wednesday, guiding her nine-piece band with a strong voice and firm directions. She’d flap her arms toward the rafters. (Louder!) She’d twirl her fists like they were socks in the dryer. (Faster!)

And was it ever loud or fast enough? Refusing to take her foot off the gas pedal, “Killing Me Softly” — her definitive hit with the great hip-hop trio the Fugees — and “Everything Is Everything” became fast, fidgety and strangely thrilling.

It felt like the inverse of what her neo-soul peers have been up to lately. Recent albums from the Roots, Maxwell and Erykah Badu have asserted their vitality by evaporating song structures, melting hip-hop and R&B into gorgeous new puddles.

Hill, however, has stiffened up. Her band raced through “To Zion” — once a poignant ode to her eldest son — like a church band after a breakfast of Red Bull. A trio of backup singers chirped high-speed gospel, squeaky keyboards sounded like basketball sneakers on hardwood, and a drum solo kept itself from derailing by incorporating the measured snare hits from Bell Biv DeVoe’s “Poison.”

Liberal with her phrasing, Hill seemed bent on proving that her songs are amorphous, living things — paintings that never left the easel. Her tweaks and left turns echoed what Bob Dylan has been doing with his songbook for decades. You think it’s like that, but tonight it’s like this.

Mileage varied, of course. The minor key reboot of “The Sweetest Thing” made it feel like it was being played back in a bad dream, while the tempo of “Lost Ones” accelerated and collapsed before Hill could find her footing.

Her rapping was more assertive with the Fugees classics “Ready or Not” and “How Many Mics,” the latter of which ended in a speedy punk-rock rave-up and a primal howl. She didn’t sound like she was performing her songs so much as trying to finally break free from them.

With an album rumored to be arriving this year, Hill closed her set with something new. “I’m a fearless vampire killer,” she bellowed over her band’s churning riffage, perhaps nodding to “Fearless Vampire Killers,” a serrated anthem by D.C. hard-core punk legends Bad Brains.

The song billowed and blustered before splashing down in a pool of cosmic slop — heavy-metal guitars grinding themselves into droning, distorted goo.

The moment called for a stage dive.

Or a leap through a bonfire.

Instead, Hill paced the lip of the stage, shaking outstretched hands, thanking her flock for renewing its vows with the great unknown.