Solution
Clean the Dust tray, transfer timing roller, and guide plates in the paper transporting paths (Main machine, A3LCT, Bypass Tray).
Clean the transfer guide plates from a feed tray, which stores the paper generating white spots, to the Paper transfer roller [A]. Normally, doing so resolves the problem.
The following picture shows the paper transporting path from the main machine (Tray1 and 2), RT5090 (Tray 3 through 5), and bypass tray to the Paper transfer roller [A].
