You are likely running out of PHP memory (and using a lot of memory in general) due to the activity level on your Pi:
[2020-10-28 20:16:00.857 41417M] Resizing "/FTL-queries" from 16515072 to 16777216
[2020-10-28 20:16:00.862 41417M] Imported 260121 queries from the long-term database
[2020-10-28 20:16:00.862 41417M] -> Total DNS queries: 260121
[2020-10-28 20:16:00.862 41417M] -> Cached DNS queries: 216059
[2020-10-28 20:16:00.862 41417M] -> Forwarded DNS queries: 34839
[2020-10-28 20:16:00.862 41417M] -> Blocked DNS queries: 9223
[2020-10-28 20:16:00.862 41417M] -> Unknown DNS queries: 0
[2020-10-28 20:16:00.862 41417M] -> Unique domains: 2216
[2020-10-28 20:16:00.862 41417M] -> Unique clients: 42
[2020-10-28 20:16:00.862 41417M] -> Known forward destinations: 2