every other block missing in chain

[wacban]

This issue happened in statelessnet. Every other block was missing despite seemingly enough stake being online. The issue appeared both with multiple validators and even with just a single validator. The repro steps are unclear.

There are two painful side effects of every other block missing:

• no block can get finalized
• chain cannot move on to the next epoch

The chain was rather troubled before the issue was triggered.

• Validators were crashing due to bugs
• The chain was stalled for a long time due to not enough stake online

There are not immediate next steps as statelessnet is down now. This is just for reference in case the issue happens again.

[andrei-near]

It happened again, similar scenario: troubled network with >30% missed chunks and network being stopped for ~24h:
Next epoch - in -2761 blocks

[andrei-near]

This seem related to #10558
near_final_block_height 119519718
near_block_height_head 119525916