Alissa Violet Arrested After Alleged Argument with Boyfriend

Alissa Violet -- a popular YouTuber -- has been arrested after she allegedly got into a ferocious argument with her boyfriend ... TMZ has learned.

Sources tell TMZ ... Alissa and Ryan Pownall went back to his apartment in Hollywood after a night out drinking at a local bar at the end of February.

When they got to the apartment, our sources say Alissa and Ryan -- who were both allegedly intoxicated -- got into an argument about Ryan's phone.

Alissa left the apartment for a time, sources tell us, but later came back, and the argument continued ... at which time, neighbors made a noise complaint to security. Later, the cops were called.

Law enforcement sources tell us ... Alissa was ultimately arrested for making criminal threats ... though they did not detail the nature of the threats.

Sources familiar with the incident told TMZ that Alissa may have had a knife in her hand -- which would explain why she was arrested, but Alissa's team has not confirmed or denied this allegation.

We're told the pair -- who dated for nine months -- broke up after the incident.

Alissa is known as a lifestyle creator ... sharing an inside look at her life filled with candid content, makeup tutorials, and more.