Shia LaBeouf's Behavior While Shooting New Movie Concerned Some on Set

Shia LaBeouf was arrested in New Orleans this week on two counts of simple battery charges ... and TMZ has learned some colleagues were concerned about him while shooting his latest film.

The veteran actor finished filming "The Rooster Prince" just a few months ago ... and TMZ is told he showed some troubling signs at times.

Our sources say that, for the most part, LaBeouf was a consummate pro ... but they say he also displayed erratic behavior ... including intense mood swings. We're told it was enough that some peeps on set wondered if he might be facing personal troubles -- especially given his checkered past.

However, one source noted to us Shia's character in 'Rooster Prince' suffers from mental health issues, and the actor really commits to his roles ... so, that might explain his behavior. We also hear Shia's arrest won't impact the film's schedule.

To be clear ... no one we talked to claims they saw any behavior like the kind we've recently seen -- no arrests, no fights -- and they're all heartbroken to see Shia's recent string of incidents. Our sources say they hope he gets whatever help he needs.

As we reported ... Shia was arrested and charged with two counts of simple battery after allegedly starting a fight, then getting beaten up outside a bar this week during Mardi Gras celebrations in New Orleans, where he purchased a $1 million home after he separated from his wife, Mia Goth.