No damage from fire and gravity

Thank you for your report!
We're already tracking this issue at MC-160464, so I will resolve and link this ticket as a duplicate.

This issue has been fixed for worlds that were not opened in that snapshot.
In order to fix it for your world, you need to execute following commands in chat (possibly need to do Open to LAN -> Allow cheats: ON -> start LAN world):

/gamerule drowningDamage true
/gamerule fallDamage true
/gamerule fireDamage true
/gamerule doInsomnia true

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Thank you