Over/underexposed images during timelapse with Sony A7rii

[moopoints]

I have been recently having a lot of issues when shooting timelapses with my Sony A7Rii. In today's test I was using a Neewer intervalometer and my camera is set to Manual: all settings are set to manual (aperture, focus, iso, shutter speed). I then let the intervalometer shoot pictures at a 5 second interval. 

 

The lighting in the room hasn't changed at all and given that the camera settings were all set manually I should have received a series of very similarly looking images. If I am not missing something then nothing should have caused any changes in exposure in the images, yet the result is that randomly some of the images were dramatically underexposed, even though the settings according to the exif data are identical. 

 

I've attached a screenshot of the exposure line of all images in the series. The blue line should have been a smooth and almost straight line given that the settings were identical and the lighting in the room hasn't changed. 

 

I've also attached a screenshot of a part of the series from Bridge, showing that some of the images are randomly underexposed. 

 

And here is a link to two sequential RAW files out of the series (the files are currently still uploading to Dropbox). They show identical exif settings yet one is strongly underexposed (the images before and after were normally exposed again). 

 

Does anyone have an idea what could be wrong with my camera or settings?

 

Much appreciated,

Jan

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