A few things.

1. Installing and removing a trigger is easy. I would put the original back in place and see what happens.

2. I would make an effort to ascertain what trigger was installed.

3. It is possible to chamber another round and have the hammer in a forward position. I had this exact same thing happen to some BM carbines in Iraq. The best conclusion I could make was that I was experiencing bolt bounce. I swapped every single part in the lower, the gas tube and the gas rings. Once I changed the barrel everything was 100%.

Not saying that this will solve the problem, but I would start by putting in the old trigger and going from there.