External image storage saves pictures with the words "Concurrent server side render limit reached"

Hi, we just upgraded to version 5.3.4 a couple days ago and we have been successfully using the external S3 based image storage for more than a year now. However, with the new version, we sometimes get images with the following words in them: “Concurrent server side render limit reached”. I have attached a screenshot.

The logs actually show that the image was successfully uploaded, but when you actually go and view the image, it’s just a picture with those words in it. Seems like a new bug?

This has hopefully been resolved in a Github issue, so perhaps it can be deleted from here?