Here's the deal ... Bam's been across the pond lately for a string of Q&A gigs he'd booked through a promoter -- where he was scheduled to talk to audiences ... all of which recently came to a screeching halt after the peeps he was working with announced the rest of his appearances were cancelled.

There's been a lot of accusations and drama brewing in the background this past week -- with allegations that Bam was acting erratic and rolling with a new crew of misfits.

Some online -- especially on Reddit -- have been claiming Bam's been indulging in booze and drugs again ... but he hopped online Thursday to deny all that, insisting not only is he alcohol-free ... but he had a perfectly good reason for canceling his shows in the UK.

Long story short ... Bam says he re-injured his knee, and that these shows are gonna get rebooked -- so it's no harm, no foul in his mind.

He does allude to some kind of physical confrontation between the people Bam's been staying with and the promoters ... but he says he wasn't in the mix for that -- so he doesn't think he did anything wrong. He also acknowledges he and his girlfriend have been fighting.

Last but not least ... Bam shoots down any notion he's been under the influence lately, pointing to the fact he's drinking tea in the video. Remember, this comes not too long after he got into a fistfight on the street here in L.A. ... so, thing have been a bit tumultuous.

Despite all that ... Bam is insisting everything's A-OK -- although, hard to say if folks buy it.