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Max Ehrich , an actor who was once engaged to Demi Lovato , is dealing with a legal mess down in Florida ... because he got arrested for allegedly getting violent with a family member.

Law enforcement sources tell TMZ ... Max was arrested Tuesday night for battery on a person 65 or older ... and the charge involves domestic violence on a family member.

We're told Max posted $1,000 bond and was released from jail Wednesday. Getty

The arrest comes on the heels of some fan concerns regarding Max's behavior ... he was on Instagram Live earlier in the day, acting erratic and making cryptic posts.

Max went live on social media multiple times Tuesday with his mother in the room ... but it's unclear if she's the family member from the battery charge.

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