Sony A6700 exposure issue with Auto ISO

[GonzaloGM]

Hi everyone, I'm having an issue that might be due to some bad config on my camera but I can't seem to find it. I'm using an A6700 with a Sony 200-600, previously I owned a Nikon D7200 with a Sigma 150-600 and for birding I used manual mode, setting shutter speed and aperture and leaving a floating ISO (Auto ISO), which worked great.

I tried this with the A6700 and for some reason the pictures come severely underexposed, so I have to mode to manual ISO so I can even properly see through the EVF. I have a wide range for AutoISO (the default one), I tried the different exposure modes, exposure compensation is at 0, so not sure what might be off. 

Today I tried testing in Auto mode and it's exposing correctly, but if I choose Shutter priority or manual mode for example, they get underexposed. I'm attaching some example images and settings, let me know if you have any idea on what I could look into, or if you want me to show more settings. Thanks a lot!

 

3711 is auto mode. 3712 is shutter priority with 1/800, 3713 is manual mode with shutter speed 1/800, aperture 5.6. 
Uploading the others to imgur because it's telling me it's more than 1000kB when it's 200kB, weird.

Here's the album: https://imgur.com/a/QUYEHGm

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[Pieter]

What ISO value did the camera choose in photo 2 and 3? What AutoISO range did you set?

[GonzaloGM]

4 hours ago, Pieter said:

What ISO value did the camera choose in photo 2 and 3? What AutoISO range did you set?

Auto range was default (it's on the screenshots in Imgur I uploaded) but it's something like 50-100500. For photos 2 and 3 it chose ISO 100. When taking the pictures it said Auto ISO until I half-pressed and chose 100.

I had tried all the metering modes and made no big difference.

I ended up resetting the camera with "Initialize" because I tried a lot of things and nothing worked. Luckily now it's working just fine.