There is a quiet kind of frustration that lives inside every spreadsheet user who has ever hit an invisible wall, and this report captures it perfectly. The user has done everything right: consistent permissions, careful file management, a willingness to troubleshoot. Yet the theme refuses to apply, not with an error message or a greyed-out menu, but with a silent, stubborn non-response. That is the worst kind of failure because it offers no thread to pull, no obvious cause to address.
What makes this account so valuable is what it rules out. The problem is not tied to file size, age, storage location, or sharing status. It is not a permissions issue, since manual formatting works fine. It is not a matter of user error, because new workbooks behave perfectly. The only consistent pattern is that once a file becomes corrupted in this way, it stays corrupted, and the only reliable fix is to copy everything into a fresh workbook. That is not a solution; it is a workaround that costs time and trust.
For users who rely on custom themes to keep their work consistent, this is not an abstract annoyance. It is a productivity trap that can strike at any moment, often when you are deep into a project and have stopped thinking about the mechanics of the tool. The fact that the user cannot reproduce the issue on demand makes it even more insidious, because it means you cannot prepare for it or test around it. You simply discover one day that a file you have been using for weeks has quietly lost its ability to change themes, and no amount of digging will tell you why.
Our take is straightforward: this kind of bug deserves more attention than it gets, not because it is flashy or dramatic, but because it erodes confidence in the very tools we rely on for precision work. The user has done the hard part by documenting the behavior clearly and honestly, including the parts they cannot explain. That is exactly the kind of evidence that helps developers reproduce and fix the issue. If you are reading this and have hit the same wall, do not assume it is your fault. Copy your work into a new file when you can, keep backups of older versions, and report the behavior with the same level of detail you would want if you were on the other side of the ticket. The more specific you can be about what you were doing when it broke, the better the chance someone can find the hidden snag.