Seen in several production clusters running 8.3 (thanks to the changes in #87881) but this also explains #86059 in earlier versions:

    [instance-0000000011] negative value in circuit breaker: [eql_sequence,limit=8589934592/8gb,estimated=-7961288

My guess is that somehow this circuit breaker is releasing bytes it didn't already hold. Seems pretty rare, and not covered by tests since it would trip assertions there.
x-pack/plugin/eql/src/test/java/org/elasticsearch/xpack/eql/execution/sequence/CircuitBreakerTests.java
assertEquals("sequence_inflight", e.getMessage());
        
        SequenceMatcher matcher2 = new SequenceMatcher(stages, false, TimeValue.MINUS_ONE, null, new EqlTestCircuitBreaker(15000));
        matcher2.match(0, hits);
        e = expectThrows(CircuitBreakingException.class, () -> matcher2.match(0, hits));
        assertEquals("sequence_inflight", e.getMessage());
        
        SequenceMatcher matcher3 = new SequenceMatcher(stages, false, TimeValue.MINUS_ONE, null, new EqlTestCircuitBreaker(15000));
        matcher3.match(0, hits);
        matcher3.clear();
        matcher3.match(0, hits);
        e = expectThrows(CircuitBreakingException.class, () -> matcher3.match(0, hits));
        assertEquals("sequence_inflight", e.getMessage());
    }
    public void testMemoryClearedOnSuccessfulRequest() {
        assertMemoryCleared(2, SuccessfulESMockClient::new);
    }
    public void testMemoryClearedOnShardsException() {
        assertMemoryCleared(stages, FailureESMockClient::new);
    }
    private void assertMemoryCleared(int sequenceFiltersCount, BiFunction<CircuitBreaker, Integer, ESMockClient> esClientSupplier) {
        final int SEARCH_REQUESTS_EXPECTED_COUNT = 2;
        List<BreakerSettings> eqlBreakerSettings = Collections.singletonList(
            new BreakerSettings(
                CIRCUIT_BREAKER_NAME,
                CIRCUIT_BREAKER_LIMIT,
                CIRCUIT_BREAKER_OVERHEAD,
                CircuitBreaker.Type.MEMORY,
                CircuitBreaker.Durability.TRANSIENT
            )