As soon as you the leader or manager detect any down fall in morale or a souring of attitudes. You and the rest of the management/ownership team must find the fault within yourselves and correct it faster than quickly. It is better for you to stop all work without any cessation in pay to find the negative source and expel it than to just continue on into the unseen ice berg.
It is better to have time lost and payroll beyond expectations than to lose the ship all because of low morale un-mitigated and un-managed by the entire leadership team.
(The content is important and not the spelling).
All attitude problems and morale issues begin and end with the entire management team. Poor performance and worker misery is just a result of you the owners, leaders and managers.