FWIW, I can still fairly easily reproduce this in mako hw, image 171, by toggling ca. every 1-2 seconds (so not "super fast"). While in the error state, the overall flight mode state can still be toggled (incl. Bluetooth and WiFi radios), but the cellular modem stays offline and shows "soft=true" in /var/lib/urfkill/saved-states (and the WWAN setting is even preserved over reboot).
FWIW, I can still fairly easily reproduce this in mako hw, image 171, by toggling ca. every 1-2 seconds (so not "super fast"). While in the error state, the overall flight mode state can still be toggled (incl. Bluetooth and WiFi radios), but the cellular modem stays offline and shows "soft=true" in /var/lib/ urfkill/ saved-states (and the WWAN setting is even preserved over reboot).