We sometimes have the same straight.el repository directory used with multiple build caches, for example when using the CI tooling from Radian to test the configuration against a different Emacs version from the host system, without having to redownload hundreds of MB of packages again (just need to recompile them, with a separate build directory and build cache). However, this causes some issues where having one instance of straight.el build Org triggers a modification in every other straight.el instance for that repository, because the pre-build step updates mtimes in the repository.

Not sure if this is something we can or should fix, but noting it down as it's a significant annoyance for me (building Org takes a long time).