When users selected hand wave, it appeared briefly (enough to be seen and not enough time really to screenshot) before the wave changes automatically to a heart.
My plane today was to re-add hand wave after having it not as a reaction and see if it made any difference.
My suspicion is that either due to addition, removal, and shuffling of reaction positions over time that (for whatever reason) wave is not recognized and so is being substituted as a heart.
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