Dealing with a bug in the language implementation is almost always a miserable experience, and all implementations have them; SBCL isn't unique or even unusual in this respect. Where it, and other Common Lisp implementations with similarly mature tooling, are indeed unusual and exceptional is in the unparalleled flexibility they offer to inspect, introspect, and instrument running code in real time, without having to so much as restart the system under inspection, and also without the constant headaches of something like gdb and its often flaky translation of byte slaw into symbolic structures.

There's a goodly number of reasons not to choose Common Lisp for production, not least of which is that engineers skilled and familiar with the language can be hard to find. Debuggability, though, is not among them.