Wagtail page uneditable after StreamField / Body Text gets too long

I'm running into a problem like this with my Django / Wagtail / CodeRedCMS site:

https://github.com/wagtail/wagtail/issues/5872

When my ArticlePage / body Streamfield content length gets to a certain point ("too long", not sure exactly), and I Save Draft, what returns is a broken / incomplete admin page with all StreamFields missing from the body. And clicking Preview returns an error: "Error while sending preview data."

I have the nagging feeling this is infrastructure based and not code-based as I can't replicate it locally, this just happens in production.

Things I've tried:

• Added DATA_UPLOAD_MAX_NUMBER_FIELDS to Django settings and tried multiple numbers (2K, 5K, 10K) and even None

• Added client_max_body_size = 5m; to NGINX config

• Tried different Gunicorn settings with more workers, more threads and using Gevent.

• Sized up Digital Ocean droplet to more powerful CPU and RAM

This is a CodeRedCMS 1.0.1 site with Wagtail 3.0.3 and Django 3.2.15 in Python 3.8.10. On Digital Ocean droplet with a DO managed PSQL database. Curious if anyone has run into this before.