Clear the Chomp app cache. Go to Settings>see all apps>Chomp>Storage and cache>CLEAR CACHE.
Problem: Sound notifications to received texts from anyone in my contacts list stopped occurring. I repeatedly tried to set alert sounds in the notifications settings for individual contacts but the changes wouldn't "stick", having reverted to the silent option every time I rechecked. I tried all the suggestions in the knowledge base article and more (!) without success.

Solution: I cleared the Chomp app cache and I'm getting sound notifications once more.