I’m sorry to say I haven’t found easy reproduction steps yet, but sometimes when I’m giving orders to the fleet, the priority setting for some orders will stop working.
If you add an order to a ship affected by this bug, it will have the default priority (50% I think).
If you click on that order and try and change it, the slider in the change-order menu works fine, but it will not be saved - the order priority display at the left (and presumably in the game data itself) will remain at 50%.
Changing already existing orders has the same problem, they simply will not change. This can be a problem as all cruisers are spawned with a strong attack-cruisers priority, and though I can delete and re-add that to set it to 50%, it’s not optimal.
It doesn’t always happen, and I’ll update this topic if and when I find out how and when it happens.