Is this by chance or did the new self-hosted backend of the compiler for debug builds become better at detecting (failing on) references to temporary memory? This seems to be the type of bug I produce very reliably ^^ - fortunately, those were jumping right into my face lately when I tried to compile with the latest Zig master!
In the latest patches to zdt I fixed a couple of of those bugs in the experimental “timezone-without-allocator” feature as well as POSIX TZ handling (Releases - FObersteiner/zdt - Codeberg.org).