Mark,
We're trying to alleviate these surges by increasing the number of in and out runners. Let me know what you think.
root@2311185cccaa:/var/www# ps aux |egrep runner.'(in|out)' mailman 26718 0.9 0.4 95080 73980 ? S 14:21 0:03 /opt/mailmanve/bin/python3 /opt/mailmanve/bin/runner -C /opt/mailmanve/lib/python3.9/site-packages/mailman/config/mailman.cfg --runner=in:0:2 mailman 26719 0.7 0.4 92300 71516 ? S 14:21 0:02 /opt/mailmanve/bin/python3 /opt/mailmanve/bin/runner -C /opt/mailmanve/lib/python3.9/site-packages/mailman/config/mailman.cfg --runner=in:1:2 mailman 26722 8.6 0.4 99840 78904 ? S 14:21 0:28 /opt/mailmanve/bin/python3 /opt/mailmanve/bin/runner -C /opt/mailmanve/lib/python3.9/site-packages/mailman/config/mailman.cfg --runner=out:0:2 mailman 26723 1.4 0.4 94628 75072 ? S 14:21 0:04 /opt/mailmanve/bin/python3 /opt/mailmanve/bin/runner -C /opt/mailmanve/lib/python3.9/site-packages/mailman/config/mailman.cfg --runner=out:1:2