Hi Mark,
Thank you for your quick response!
When setting up Mailman 3, I went through much of this "how to" guide here: https://wiki.list.org/DOC/Howto_Install_Mailman3_On_Debian10.
As far as I can tell, my current setup appears to be proxying from Nginx to Gunicorn, according to the related Nginx and mailman3-project-specific Gunicorn config files. Specifically, I checked the local address:port being used in the Nginx file and compared that to the mailman3-project-specific Gunicorn bind address. It looks like I might have "separated out" the REST API to a different server block in the Nginx config file, so I think I'm looking at the correct server block with this conclusion.
For what it's worth, I don't recall this type of "slow first visit startup" issue happening in the past when using web applications with uwsgi, and I've had the opportunity to use uwsgi with a variety of programs. I think Gunicorn is fairly new to me. I do, however, remember that something like this might have happened in the past when using Passenger (https://www.phusionpassenger.com/) a long time ago, but that might have been setting related on my part.
Okay, thanks for the encouragement about the potential solution to periodically accessing the related "example.mailman.site/mailman3/lists/" type location (from my earlier email). Wanted to check on that and was also hoping that there might be some setting I'm missing in the overall Mailman 3 project setup related to the "slow first visit startup" issue.
Thank you!