12:01 PM PT -- A rep for Amazon MGM Studios tells TMZ ... "Dwayne Johnson and Seven Bucks have been incredible partners on 'Red One' -- a film that audiences of all ages are going to love this holiday season. Our testing has been very strong -- the reaction from CinemaCon speaks for itself -- and we couldn’t have made it without Dwayne’s constant work and support."

They add, "Any reporting that implies that we got to this point with him showing up 7-8 hours late to set is both ridiculous and false."

The Rock got into a tiff with Ryan Reynolds while they were working on a movie together years ago -- and while it wasn't a blowup fight as has been suggested, it was a real thing.

Production sources with direct knowledge of the incident tell TMZ that Ryan -- who was the lead in their 2021 action flick "Red Notice," opposite The Rock and Gal Gadot -- did, in fact, confront Dwayne while they were shooting in 2020 ... at the height of the pandemic.

While The Wrap -- which first reported this -- claimed it was a "huge fight" they had ... our sources say it wasn't nearly as dramatic, but that RR did have a talk with his costar.

We're told there's some truth to the notion Ryan was upset The Rock was repeatedly late to set ... something that came to a head when Ryan spoke to him about it, which we're told was affecting the shooting schedule and the production at large during a complicated time.

Remember ... in the thick of COVID, film sets had strict protocols that made it difficult to film as is -- so with The Rock running behind, our sources say it eventually became an issue.

In any case ... we're told the two men talked and that Dwayne came back to work the very next day -- the shoot continued without further issue. We're told Ryan and The Rock didn't let their headbutt moment derail things ... they got on with the film, and press afterward.

As for where things stand now ... one source with direct knowledge tells us they're all good -- and that whatever concern there was at the time was dealt with professionally. More importantly, we're told their chat didn't torpedo the movie at all. As for the exact number of hours The Rock was supposedly late ... our sources say it's been greatly exaggerated.

You can glean as much in the fact that 'Red Notice 2' is reportedly in the works with Netflix ... as it was a huge hit for the streaming giant, and it still holds a major record there.

FWIW, The Rock is being accused of repeated tardiness on a new movie he's working on for Amazon ... but the studio flatly denied that, telling The Wrap there weren't any problems on set as a result of The Rock, and that they were grateful to have him aboard as a partner.

Netflix also didn't lean into any reports of a clash with Ryan -- calling DJ a "consummate professional." We've reached out to Amazon and Netflix too ... so far, no word back.