zombienet-cumulus-0005-migrate_solo_to_para has been failing consistently.

File:

Expectation

This test spawns two parachains with the same para id but different genesis, dave and eve. Node dave will produce blocks and after a few blocks output custom head_data through the PVF. This head_data contains the header that matches node eves parachain, which should now start producing blocks.

Reality

Dave starts producing blocks, but after the custom head data is submitted, eve does not start producing blocks. Instead dave continues to produce blocks.

Investigation

The culprit seems to be #4880, before that PR the test was passing consistently. The question is why the custom head data presented by dave is not set as included head.
In the logs the following messages appear a lot:

2025-01-09 17:56:06.013 DEBUG tokio-runtime-worker parachain::collator-protocol: Collation having parent head data hash 0x9fd4…10d8 is blocked from seconding. Waiting on its parent to be validated. candidate_hash=0xe666001ec78a5546c0ee6ad7723ebcb34ef3e3245fc752c5ed9bfa386c17f214 relay_parent=0x045189b697186a3ea5f0ae67aba091a1ceb7c760590b6036a5ddca6d0f593a5a traceID=306252055748700830037795645451537398963

Apparently some seconding limit was reached and the block in question not included. Modifying the lookahead collator here to build always only a single block fixes the issue and makes the test pass:

cc @tdimitrov any ideas what is happening here?