I also wonder if backups interfere with the cleanup process.
Based on everything I’ve read, the T directory is cleaned based on the last-access time. But if you’re cloning your system, and those directories get backed up, then the last-access time is the time of your last backup. Which would clearly interfere.
I wonder if this might be the case, because I haven’t had a successful CCC backup since September due to a BridgeOS panic that happens (see Post-14.7 kernel panic). Ignoring the fact that I need to install the latest macOS 14.x or 15.x, it may be significant that I’ve only been backing up with Time Machine (which only backs up the 0 directories, not the C or T directories) since then.
I wonder how hard it would be to install a wildcard filter to not back up /private/var/folders/*/*/C and /private/var/folders/*/*/T. If routine backups don’t touch those folders, they won’t change the last-access times of the contents and the self-cleaning mechanism may work better.