First of all I want to thank you guys for helping me identify my eel. I haven't felt this kind of help in a small community anywhere else.
Now for the tetra's we had a dissappearing issue when we had a rainbow shark. We ended up getting rid of the shark and getting tetras till we had 20. Now we're down to 12. I currently have 3 swordtails, 2 loaches, a small brisslemouth pleco and a larger pleco that survived. Plus 2 eels, one that was answered here and another is a zigzag eel.
Am I having a problem with hiding spots? I know I don't have enough plants. I'm thinking of getting more moss and covering the area under the wood structure on the right.
Or are they getting sucked up the filter? I thought this but couldn't find any evidence in the filter system. Any advice would be fully appreciated.
Here's the pleco I'm questioning. 
Hopefully it’s not a bobbit worm…
Oh f how would I know?!
Set up a security camera? Though they usually get in by eggs having been attached to corals/plants. Have you put any new plants in in the past few months?
Pretty sure Bobbit worms only survive in salt water. They are typically introduced in coral and live rock to reef tanks. Highly doubtful that's what you have going on here.