smtp-amavis unix - - n - 2 lmtp
maxproc does not match $max_servers.
-o smtp_data_done_timeout=1200 -o smtp_send_xforward_command=yes
These are the wrong options for an lmtp service. This is why you see:
Beyond that, delays of 120s and 300s look suspiciously man-made. I don't have a concrete idea, though. This may be a question for postfix-users (together with related logs from vmail2).client IP address unknown, fetched from Received: 127.0.0.1
