the admin is based on a mapping (defined in the admin ).
That mapping has to parts, a directory and a lucee archive (.lar file).
For every request /lucee/admin lucee FIRST check if the file exists in the physical direcrory, what is "ROOT/WEB-INF/lucee/context/admin" and only if not it check the archive for the file.
So the solution is very simple, to solve the issue simply copy the files did change to the directory (see above), then lucee wull pick this files and not go into the archive.

Thank you for such prompt action!

Do you think you could create a patch just for this issue or create an instruction on how I can patch it myself? I can't upgrade the server without a full testing cycle for big number of apps, but I would be cool to fix this problem. It isn't a big deal, just a merely an annoyance because it trips "missing template handler" and creates unwanted noise.

I've analyzed this ticket & confirmed the issue happened on lucee 4.5 & 5.2 versions. Added the missing image file into the admin.

Pull Request: https://github.com/lucee/Lucee/pull/508