Electrical wiring to indoor light switch -- two black hot wires or one line/load wire?
Switches have 2 "sides": Supply (always-hot) and switched-hot onward to the light.  

The "same wire" wire notably stops here and goes to another switch. Only always-hot/supply will do that.  So we just ticked that box; we now know what it is.  

The other two wires on your old switch must therefore both be switched-hot. That's unusual but not impossible.  Noting that you have 3 lights and 5 lights acting somewhat independently, my guess is that one of those wires feeds the 3 lights, and the other one feeds the 5 lights.  

Anyway, those wires were together before.  Note they were both touching the same metal plate before, thus connected before.   You decided to separate them, I'm not sure of your reason and maybe you aren't either.  But if you want it to work like it did before, don't separate them :)