Same problem after Big Sur installation with iMac (Retina 5K, 27-inch, 2019), few BSODs in a last week... userspace watchdog timeout: no successful checkins from com.apple.logd in 120 seconds panic(cpu 2 caller 0xffffff8013f6ea25): userspace watchdog timeout: no successful checkins from com.apple.logd in 120 seconds service returned not alive with context : unresponsive dispatch queue(s): com.apple.firehose.io-wl  service: com.apple.logd, total successful checkins since wake (3900 seconds ago): 379, last successful checkin: 120 seconds ago service: com.apple.WindowServer, total successful checkins since wake (3900 seconds ago): 380, last successful checkin: 110 seconds ago ... & so on