I have a very odd problem with my new NodeBB forum.
All static images (such as profile pictures and the favicon) will randomly disappear from time-to-time, only for all of it to come back a few hours or days later.
Nobody in this first image has a profile picture. This is from the first disappearance of all static images. Manually uploading new profile pictures or a new favicon asset simply does nothing and keeps the default NodeBB placeholders.

This second image is from when it all came back a few days later (including the favicon).

The logs in the admin dashboard reveal nothing other than an error related to the Harmony theme (which I am not using).
Any ideas for what may be the cause as well as the solution? All feedback is greatly appreciated, because I'm at a loss.

Thanks in advance.

julian I'm not using a separate volume, no.
It's all contained within a single Ubuntu server.
I have my forum running through a Docker instance, however. I'm not very experienced with Linux, but I doubt that being run in a Docker instance would be the cause for any problems like what I'm experiencing.

julian Doesn't look like I can.

Chrome is reporting a load error, and going to the direct image URL just shows text saying "Not found."
Any way I can debug this further? Permissions for the forum aren't being changed by anyone each time the assets become available/unavailable.

Thanks.