As a side tip for anyone who is upgrading, remember you can do the 'exec reassesschains' if you end up at a lower height than us (it worked for me) due to LLMQ errors.
In the latest version I increased the LLMQ start height to 170,000.
Starting up LLMQ is much trickier (and dangerous) than I expected.
Since LLMQ drives chainlocks, the wallet is going to throw a bad block error, mark the block as dirty and put the wallet in a non recoverable state if it finds any block greater than 170,000 that is not in a quorum.
What this means is either the network has a lot of sancs, and a healthy quorum environment, or absolutely fails with a nightmare scenario.
This is obviously a decision Dash made to ensure there are no exceptions to the quorums once they are up and running.
So in the current state of testnet, we would need to try to bring one more sanc on before 170,000 and see if a quorum forms, otherwise we need to keep increasing the LLMQ height.
What frightens me is if we start the quorums and then take down 70% of the nodes. I think that means, we will need to regroup and bring the sancs back online.
But from what I see, if lets say we lose those sancs VMs, and recreate them all, then the sigs will be new and the old quorums will be invalid (and I think that means a chain rollback). We will cross that bridge when we come to it as our prod environment should be OK, as its always going to have for the most part more than 100 reliable sancs, so theoretically the quorums will never fail.