Canon EOS R & R6 AUTO ISO issues

[JAYSTATON]

Both my EOS R & R6 can occasionally change my set ISO to "AUTO ISO".  I NEVER use "AUTO ISO".  EVER!  So when my images suddenly change in exposure, it is troubling.  I am a wedding photographer and shoot a lot of sunset newlywed portraits on the beach.  I always use off-camera flash set at manual, so I know when the exposure quickly changes without me initiating the change.  When it changes to AUTO ISO, I quickly change the ISO back, but then the camera changes it back to AUTO ISO.  I have had to set my camera's max ISO to fix the issue.  But then I have to change it once I go back to the reception. 

Anyone else have this issue?

[Waddizzle]

Sorry to hear that you are having issues with your gear.

Since you are reporting the same issue on two different camera bodies, I am inclined to look for a common denominator.  In other words, I am basically asking for more details about your shooting conditions, lenses, any mount adapters, and exposure and camera settings.  

Tell us how to reproduce your issue.

1. What shooting mode(s) are you using?  Are you using a flash?
2. Does the issue occur with more than one lens?  What lens?  
3. Are you using a Canon mount adapter with EF-mount lenses?  Canon lenses?

That is sufficient for now.  No need to dive deep into the weeds, yet.  Tell us how to reproduce your issue.