I'm new to aquariums and fish keeping. I have a 40 gal tank set up. I had around 5 guppy, 3 Glass catfish, 3 glofish tetra, 3 mollies, two Bala sharks, and three neon tetras, and one threadfin rainbow (beautiful one)

I had those for about three weeks, everything was fine.

Then, I added three rubber nose pleco, and that was fine.

Finally, I added two dwarf gourami and two glofish sharks... Then I was on travel for 4 days, but the fish were fed during that time. When I came back, I noticed some fish missing.

Upon inspection, I found a spine in one of the little decoration hiding spots I had, so I knew something had are that fish... Then I noticed, two more fish were stuck in the wat e filter (their body was intact). I'm guessing they died and the water current sucked them there.

Immediately my culprit was the glofish sharks, so I returned them.

During this, one guppy was very injured / sick which died the day after, the other healthy guppy disappeared too. at this point all of the guppy had died

After I returned the glofish sharks, I got three Cory catfish, but the panda Cory died a few days later where the other two were healthy. I also got a south African cichlid and a German blue ram.

Today I noticed my three neon tetra are missing, and I found the body of the rainbow threadfin.

Which fish seems the most likely culprit? Did I mess up the grouping?