Speedlite 600 EX II-RT inconsistent firing in manual

[Annette1]

I use my Speedlite in manual mode, on camera, for wedding reception candids. I noticed that I will get some great exposures and then about 5 or 6 shots later the image is blown out with no changes to any camera or flash settings and shot from similar distances. Any suggestions?

[rs-eos]

Are you sure the flash is in manual mode?  How about your camera? Is it in manual mode as well?  I'm wondering if say auto ISO is kicking in on occasion?

[Annette1]

I am using all manual settings both on my flash and camera. ISO is in manual as well.

[MikeSowsun]

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@Annette1 wrote:

I use my Speedlite in manual mode, on camera, for wedding reception candids. I noticed that I will get some great exposures and then about 5 or 6 shots later the image is blown out with no changes to any camera or flash settings and shot from similar distances. Any suggestions?

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Can you post some examples? 

Are you using bounce flash or direct flash?

Are you using some kind of a modifier?

[Annette1]

I'm using direct flash, no modifier. I will post some samples.

[Annette1]

[Annette1]

No changes in settings. Top image shot first.

[MikeSowsun]

The distances look different. What is the focal length used in each photo? Can you provide the EXIF data for each photo? 

[Annette1]

[Annette1]

The distances are a bit different but if that were the issue then the image with the people closer to the camera should be more overexposed with the one with more distance under exposed.