Any suggestions how to see what is going wrong?
Issue `masternode list` from time to time to see if all your masternodes are present on the list.
After starting them they all appear in masternode-list, but after some time some of them disappear. Most of the time already the same day.
What if you manually re-run start-many? Do they return? If so, the dirty mitigation is to run this command within an infinite loop (with some reasonable delay to avoid useless processing).