Truncation of http responses

Hi there, We recently upgraded to 3.9.9 and have been experiencing seemingly random truncation of http responses. That is to say the source that the browser receives is cut off at some point (not always at the same point), and none of the script/css/code below that point is loaded and the page breaks in various ways such menu items displaying as text on screen, or the course curriculum menu/accordion not responding to clicks. Many of our students and clients have already experienced in the issue in a live environment. While we have video of the issue occurring, including the developer console, we have not been able to find a way to consistently replicate the issue. In most of the cases we've had it occur, it has been within a course as either a student or admin user. However, in one case it occurred on the course admin page. Sometimes it occurs on the first page load inside a course. Other times it occurs on another unit in the course. In most cases, refreshing the page, or navigating away and coming back will not get rid of the issue. Clearing browser cache also seems to have no effect. Sometimes, marking a prior unit in the course curriculum complete and then navigating to the next unit seems to fix the issue. This leads us to believe that it might relate to how units are marked complete in the course (e.g. first unit is not marked complete, but subsequent ones are). We've investigated the rest of the stack (nginx on alpine linux, containerised on AWS ECS, sitting behind an ALB and Cloudfront) and have been unable to locate the issue there. Is this something you have seen occurring with WPLMS before? Prior to the upgrade, we were not experiencing the issue. I will post a link to the video and other screenshots, as well as login credentials in a follow-up private post. Thanks for your help.