After updating to the "lisp-team" branch which included an updated sbcl and more (commit 2d5a7bfed5ccae6ce8adbef3ae1017d6ce8512be), my system broke down when reading ~/.stumpwm.d/init.lisp with a message like "failed AVER: (= (ASD (LENGTH KV-VECTOR) -1 ... This is probably a bug in SBCL itself. ..."
Got a hint to read https://git.sr.ht/~freakingpenguin/rsent which references https://issues.guix.gnu.org/62890. I tried with --no-grafts as that repo does, and my system works (commit e32e3d0a03dc17c4c54a91aad053c9036998b601).