Auto ISO is determined only according to the ambient. The flash merely reacts to whatever the ISO it discovers to be in effect, and the TTL part tries to match the flash power to the scene that way.
Auto ISO value is not about the flash. Auto ISO is about only the ambient. My notion is the only thing that could have changed is the ambient level present. Or the f/32 effect on the ambient might be new.
If it is not doing what you want, you can turn Auto ISO off.
There are other model differences though, regarding Auto ISO.
Older DSLR models, up through the D300 would not let Auto ISO increase at all if it detected we were using flash. Because, we were using flash instead.
Then Nikon got the bright idea to change that, and starting with the D300S, Auto ISO would fully increase according to the ambient, and if Auto ISO, the flash generally always had to work into the highest Auto ISO.
But then they learned again, and starting with the D800, now Auto ISO is only allowed to increase two stops (typically to ISO 400) if flash was discovered present. ISO 400 is generally good with bounce.
Two exceptions ...
That is speaking of external hot shoe flash. The internal flash does not limit Auto ISO, and will still let the ambient go to very high ISO (according to ambient). Auto ISO value is still not about the flash however, it is determined by the ambient, at whatever aperture and shutter speed. Flash is not affected by shutter speed, so you could lower shutter speed to help the ambient, and then see lower ISO. But the best thing with the most control is to turn Auto ISO off with flash.
And another exception to all above is that if the flash itself is in manual flash mode, Auto ISO will never increase. Manual flash cannot react to ISO changes. TTL does react with power level changes.