There have been 3 significant problems (2 of them LLVM changes that Zig hasn't adapted to) that have been multi-day frustrations.
We are currently holding at 0.15.1, partly because of the I/O changes (although we're not heavy users of I/O), and partly waiting for the native backend implementations to stabilize.
All that said, we remain very happy with the choice of Zig - it has so many advantages over C/C++ and even (for our application) Rust (we have about 3K LOC in our original Rust implementation).
Is Zig fully mature? Certainly not! Is it mature enough to be highly productive? Certainly!