Hello.
When I'm shooting in real low light and using a high ISO, I keep getting lines in my photos. Please see attached photo as an example. Does anyone know why this happens? This is my first mirror camera and have never had this issue before.
Need to see more examples in different conditions with EXIF included and what shutter mode you were using (electronic, first curtain, mechanical). Would also love to see the same photo take with lower ISO settings and different shutter speed.
Knowing nothing other than what I see in front of me I can posit a lot of possibilities, including an ultra high rate of light flicker that is captured perfectly by the sensor sweep at this specific shutter speed, the same sweep responsible for rolling shutter in other types of shots. If you're only seeing it in this conditions at a particular shutter speed I suspect that's more your problem than low light and high ISO, but more information and examples will tell the tale.
EDIT: were you in electronic shutter? I can TOTALLY see that being an issue.
Stage lights like those are often multicolored. You can set them to do changing patterns and so forth, and by nature they are emitting a mix of colors at any one time. Our eyes blend a lot of things together automatically, but the camera doesn't. A longer exposure can force that blend to happen on the sensor.
LED animated signs also give some really strange effects at high shutter speeds.
The R5 sadly only has the regular anti flicker, not the high frequency variant the R6II/R8 have. The HF anti flicker almost magic, but you have to recalibrate it almost every shot in dynamic environments.
I hope new bodies will gain a "continuous update" mode for HF anti flicker, that would make things a lot easier for me. Especially during the winter season where most of the pictures I take are indoors with LED lighting. And it's not a candid anymore if the shutter clack alerts my kids after the first picture