Images Fail to Load, net::ERR_CONTENT_LENGTH_MISMATCH

When you request data from a web server, it responds first with some information about the data (HTTP headers) and then with the data. One of these pieces of information, an HTTP header, is called Content-Length. It tells the client how much data it should expect to receive from the server. When your browser gets an image, the server's response (very simplified looks like)

Content-Length: 100000< the image, 100000 bytes of data >

The client knows the request is complete when it has received the amount of data told by Content-Length. Until it receives in this case 100KB (100000 bytes), it considers the image, for example, to not be done loading.

If the server breaks the request before the client receives the data from the server, or if the client receives more data than it received, the client will throw some sort of error and assume the data to be corrupted/unusable and dispose of it. How this is handled can vary between browsers.

How did you upload the images to your website? Myself, I have encountered this problem in a situation where the file's supposed size was stored in the database, and this was used to set the Content-Length header. The file size in the DB wasn't correct for the file. HOWEVER, I know that WordPress does not store file sizes in the database; media uploads are simply represented by a URL.

This could also happen if the web server runs out of resources and can no longer fulfill your requests; you said you had lots of images per page. If you are on a really lousy shared hosting plan, it may be the case that the host imposes limits, or that the server simply can't handle the traffic of all the sites it hosts.

I wanted to circle back on this in case someone else is experiencing this problem. It appears that there is some type of glitch between HTTPS and image retrieval that was causing the problem. While I don't understand WHY that is, I converted my site from SSL/HTTPS to simple HTTP (which I was able to do as it doesn't require encryption) and it appears all images load as they should.

If someone understands the "why", I'd love to understand what the issue actually is. Luckily, I was able to come up with workaround. So, while this doesn't answer my question, it does provide context of what is causing the problem and my common sense workaround.

You might see this problem with a shared hosting service. Free bandwidth is like free speech, not free beer. Resource outage policies are invoked during traffic spikes.

A distributed system architecture solves this by inserting a front-end CDN tier (eg. CloudFlare). CDNs cache your static resources and can vastly reduce the load on your host. In fact, for completely static sites the host can be shut down.

There are other advantages to CDNs, like attack detection, free SSL (not beer) and overall improved performance and security compared to shared hosting alone.

Many CDNs are free (as in speech). You could also upgrade to private hosting, but $ and you still might want a front-end tier.