Traffic is passing through the network; however, not all devices are communicating between them.

Unable to access the SRX from the device "A"; even though, there was traffic passing from device "A" to device "C" which is behind the SRX.

Make sure the policies are correctly configured.

If no dynamic apps are used, you do not need the command line:

set security policies from-zone {zone_name} to-zone {zone_name} policy {policy_name} match dynamic-application any

That is because the policy forces the traffic to match any dynamic application to match such policy. So, if the traffic does not include any dynamic application, the traffic will not match the policy and not be permitted.