Photoshop, go home, you're drunk.

[Darkerkat]

 generative expand gone rouge... I guess I have too many files open? 

[c.pfaffenbichler]

Does turning off »Use Graphics Processor« in the Performance Preferences (Photoshop > Preferences > Performance > Graphic Processor Settings) and restarting Photoshop have any bearing on the issue? 
Does turning on »Deactivate Native Canvas« (Photoshop > Preferences > Technology Previews) and restarting Photoshop have any bearing on the issue?

[D Fosse]

I have never used generative fill so I can't help you there.

But in this case, it shouldn't be necessary. It should be simple enough to transplant another area with some small adjustments to make it blend.