Running Solus with kernel 4.18.16-96. In journalctl, the following is logged at boot:
oct 30 14:24:19 pt-00611 kernel: cfg80211: Loaded X.509 cert 'sforshee: 00b28ddf47aef9cea7' oct 30 14:24:19 pt-00611 kernel: platform regulatory.0: Direct firmware load for regulatory.db failed with error -2 oct 30 14:24:19 pt-00611 kernel: cfg80211: failed to load regulatory.db
Error is gone after copying regulatory.db and regulatory.db.p7s to /lib/firmware/.
Files can be obtained here: https://mirrors.edge.kernel.org/pub/software/network/wireless-regdb/