I noticed Safari has a file size of 1.3 gigs on my iPad 5th generation. It was formally a fraction of that size. The only thing I have done differently was to sign up and receive iOS 12 public beta.
Yes, I have cleaned out the Safari cache, and even deleted the profile, but no joy. Any suggestions would be welcome.
File a bug report. You’re running a beta and mis-reported file size is not un-heard of. On High Sierra beta my MBP always reported being almost half the size it really was. In the final that was fixed.