Poor video quality from Canon 5D mark II

[Pavlos Kapa]

Hi all,
I noticed couple of times -while shooting in low light (using 4000-6000 iso) with Manual mode on 24fps and 1/50 shutter speed- horizontal wavy lines from the top to the bottom of the footage, mainly on the darker parts of the image. The lines were more noticable when I shot in gig space where green ad blue lights are on. Any suggestions for solving this?

Thank you