There is no bond screw on this neutral bus but there is one on the other neutral bus. I did not see a jumper strap between the two buses. My thinking is there needs to be a bonding screw here. Looking for a second opinion.
The two neutral buses need to be connected together. I would bet there is a flat metallic jumper under that mess of wire. If they are not connected together then a bond screw in the second bus would not be permitted to correct the problem because the enclosure would then be part of the path of the neutral current.
If there is a jumber bar then it would be behind the main breaker. I did not see one but your right, could be behind the wires. Can you clearify for me? One screw plus jumper to the other bar is OK but cannot have a second screw if no jumper is installed?
It looks like there may be a jumper bar in the second image behind the main breaker.