The rules are clear about "willingly" ending a move in an occupied square:
"Whether a creature is a friend or an enemy, you can’t willingly end your move in its space."
But they aren't as clear when it comes to sudden changes in size (such as those from a Wild Shape into a larger creature, or when under the effects of an Enlarge Person). If such an effect results in the character instantly sharing the same square(s) as other creatures, what happens? Do they get pushed back to an unoccupied square? Or is the character forced to an unoccupied space (assuming one exists)? If no such unoccupied space exists, is everyone suddenly considered 'squeezing'?