Mine is also on a Pi4 using the Channels Pi image (2021.0224.1817). I didn't have the opportunity to dig around the system to see if there are any logs that show what happened. From what I can tell, it had finished a recording and hung up sometime during the commercial skip processing. When I went to watch something later in the day, the Channels app gave me "your DVR is not available" screen. I had to hard restart the Pi a few times before it booted past a twice-flashing green light. Here's the DVR log as an FYI...
2021/04/25 10:31:00.031387 [TNR] Closed connection to 107AF30D/0 for ch3.1 KYW-TV
2021/04/25 10:31:00.075940 [SNR] Statistics for "TV/CBS News Sunday Morning/CBS News Sunday Morning S2021E17 2021-04-25-0859.mpg": ss=67%,58%-72% snq=97%,72%-100% seq=100% bps=13147112,1601760-16923008 pps=1248,152-1607
2021/04/25 10:31:00.091510 [DVR] Finished job 1619355540-19 CBS News Sunday Morning
2021/04/25 10:31:00.165530 [DVR] Processing file-530: TV/CBS News Sunday Morning/CBS News Sunday Morning S2021E17 2021-04-25-0859.mpg
2021/04/25 10:31:00.320478 [DVR] Waiting 4h27m59.679547771s until next job 1619377140-20 NHL Hockey
2021/04/25 10:31:04.605874 [DVR] Running commercial detection on file 530 (TV/CBS News Sunday Morning/CBS News Sunday Morning S2021E17 2021-04-25-0859.mpg)
2021/04/25 15:06:58.389464 [SYS] Starting Channels DVR v2021.04.22.0122 (linux-arm64 pid:305) in /mnt/data/channels-dvr/data
2021/04/25 15:06:58.782203 [SYS] Started HTTP Server
2021/04/25 15:06:58.832975 [SYS] Waiting on dependencies network-online.target time-sync.target
2021/04/25 15:07:03.265955 [SYS] Waiting on dependencies time-sync.target
2021/04/25 15:32:59.234325 [SYS] Done waiting on dependencies
2021/04/25 15:32:59.787855 [HDR] Found 1 devices
2021/04/25 15:33:00.722959 [ERR] Failed to request m3u: Get "http://127.0.0.1:8080/playlist.m3u": dial tcp 127.0.0.1:8080: connect: connection refused
2021/04/25 15:33:07.080753 [DVR] Recording engine started in /media/DVR
2021/04/25 15:33:07.082271 [SYS] Bonjour service running for dvr-server.local. [192.168.1.213]
2021/04/25 15:33:07.259104 [DVR] Starting job 1619377140-20 NHL Hockey on ch=[10.1]