I use a D5600 and always use aperture priority with as low an ISO that I can get away with. Recently, whenever I use a tripod the camera randomly over-rides this setting (but not always) and chooses an absurdly ISO in the range of 8000-25000, even in normal light situations. The only things I change are: 1. I turn of the VR; 2. I delay the shutter release by 2 seconds. 3. I would typically set a very high aperture of f22. Nothing else is changed, yet this issue NEVER occurs with hand-held shots. I'm pretty certain that I'm not making any other changes, as shots either side of the tripod shots are fine. EXIF data confirms this.
As I said, this only happens sometimes and there doesn't appear to be any pattern. Any ideas?