Good news 2.4.0.0.0 
is out and set to activate at block #791551 on mainnet, you can track the exact time of activation here. More context here.
Please note that the Stacks 2.4 Testnet activation height occurred before the finalized SIP-024 updates and release of the stacks-node versioned 2.4.0.0.0. The final 2.4.0.0.0 node is incompatible with the version that was running on testnet last week during 2.4 activation, this means that the Stacks testnet will undergo a deep reorg when 2.4.0.0.0 is released.
What this means to you:
Blocks mined after testnet BTC block 2,432,545 will all be considered invalid by 2.4.0.0.0 nodes and upgrading Testnet to the 2.4.0.0.0 release will require resetting your node to a chainstate snapshot from before that height.
Nodes will recognize that an affirmed PoX anchor block is missing, but should recover automatically.
We will be resetting the Stacks Testnet to a chainstate before 2,432,545 as we upgrade to 2.4.0.0.0.
You can follow the progress on testing for 2.4 here
PS: This only affects Testnet, 2.4 hasn’t yet been activated on mainnet.
Update:
The stacks-node currently doesn’t seamlessly recover from the unexpectedly absent PoX anchor blocks in testnet, so it needs to apply affirmation map overrides using the overrides table:
echo 'INSERT INTO overrides (reward_cycle, affirmation_map) VALUES (413, "nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnppnnnnnnnnnnnnnnnnnnnnnnnnpppppnnnnnnnnnnnnnnnnnnnnnnnpppppppppppppppnnnnnnnnnnnnnnnnnnnnnnnppppppppppnnnnnnnnnnnnnnnnnnnppppnnnnnnnnnnnnnnnnnnnnnnnppppppppnnnnnnnnnnnnnnnnnnnnnnnppnppnnnnnnnnnnnnnnnnnnnnnnnppppnnnnnnnnnnnnnnnnnnnnnnnnnppppppnnnnnnnnnnnnnnnnnnnnnnnnnppnnnnnnnnnnnnnnnnnnnnnnnnnpppppppnnnnnnnnnnnnnnnnnnnnnnnnnnpnnnnnnnnnnnnnnnnnnnnnnnnnpppnppppppppppppppnnppppnpa");' | sqlite3 ./xenon/burnchain/burnchain.sqlite
and
echo 'INSERT INTO overrides (reward_cycle, affirmation_map) VALUES (414, "nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnppnnnnnnnnnnnnnnnnnnnnnnnnpppppnnnnnnnnnnnnnnnnnnnnnnnpppppppppppppppnnnnnnnnnnnnnnnnnnnnnnnppppppppppnnnnnnnnnnnnnnnnnnnppppnnnnnnnnnnnnnnnnnnnnnnnppppppppnnnnnnnnnnnnnnnnnnnnnnnppnppnnnnnnnnnnnnnnnnnnnnnnnppppnnnnnnnnnnnnnnnnnnnnnnnnnppppppnnnnnnnnnnnnnnnnnnnnnnnnnppnnnnnnnnnnnnnnnnnnnnnnnnnpppppppnnnnnnnnnnnnnnnnnnnnnnnnnnpnnnnnnnnnnnnnnnnnnnnnnnnnpppnppppppppppppppnnppppnpaa");' | sqlite3 ./xenon/burnchain/burnchain.sqlite
Should be sufficient to get the stacks-node to ignore the relevant invalidated anchor blocks.
More Context