Just a thought: Some time ago :wave: was changed to :waving_hand:. While both still work in posts 
both work, the official name used in autocomplete now seems to be :waving_hand:.
I wonder if your deleting and re-adding caused the configuration to be waving_hand now while it was wave before and if the latter caused the problem.
You could check the old configuration in the staff action logs: admin/logs/staff_action_logs?filters=%7B"subject"%3A"discourse_reactions_enabled_reactions"%7D