Frogs are dying

Frogs are dying from mysterious damage. I have multiple frogs in an enclosed terrarium and they are constantly disappearing. At first it seemed like they were despawning. However when I stayed in the area for an extended period of time to see what was happening I could hear some of them making taking damage noises, and then I would have fewer frogs in the area. Unfortunately I couldn’t see what they were taking damage from. So I don’t know if they are getting stuck in blocks and suffocating or drowning in the pond. I also have fish and turtles in the terrarium and they are unaffected by whatever is killing the frogs. I have replaced the frogs many times and they eventually die off, this has been ongoing for a couple months at least. 

blocks I have in the terrarium are:

dirt, course dirt, mud, moss, mangrove tree with roots, wood stairs. Wood slabs, wood fence, cobblestone, glass blocks, sea grass, coral of various types, small drip leaf, large drip leaf, glow berry vines, vines, sand, Lilly pads, moss carpet, grass, ferns, chests, water, doors. Glass panes, chain, lanterns, sea pickles, kelp.