Sync committee participation sometimes fell down 50% for few slots in the epoch

[nazarhussain]

Describe the bug

Observed randomly among different runs of simulation tests that sync committee participation fell down the 50% for few slots in the epoch. Which end up having less than 90% average for the epoch with the epoch length of 8 slots for minimal preset.

Slots which are not listed in table below have participation values 1.

Slot	node-1-beacon-lodestar	node-2-beacon-lighthouse
1	-	-
2	-	-
3	-	-
13	-	-
14	-	-
15	-	-
16	0	0
17	0.40625	0.40625
18	1	1
19	1	1
20	1	1
39	1	1
40	1	1
41	0.40625	0.40625
42	1	1
43	0.40625	0.40625
44	1	1
45	1	1
46	1	1
47	1	1

Expected behavior

There should be 100% participation for all slots except the first slot of the altair fork.

Steps to reproduce

Run sim tests in multiple times.

Additional context

Check the multi-client logs for the following sim-run attached.

debug-test-logs-cli (11).zip

Operating system

Linux

Lodestar version or commit hash

unstable

[nazarhussain]

For reference this issue is not new and I observed this behavior many times earlier as well. But in multi_fork test because we have 5 nodes, so low participation for 1 or 2 nodes in few slot does not reduce the epoch participation below 90%. In multi-client test we have only 2 nodes, so why this impact a lot in this test.

[nazarhussain]

We should revert this change when this issue is fixed.

lodestar/packages/cli/test/utils/simulation/assertions/defaults/syncCommitteeParticipationAssertion.ts

Lines 6 to 8 in 5047410

	// Until we identity and fix the following issue, reducing the expected sync committee participation rate from 0.9 to 0.75
	// https://github.com/ChainSafe/lodestar/issues/6432
	export const expectedMinSyncParticipationRate = 0.75;