When disease megaevent occurs, all abilities including logistics are lost. So what happens to fleets? If you click on them, there are no ships. OK, I thought to myself, not to worry, after I cure the disease, my ships will come back.
That is where the bug comes in.
I have cured the disease and I still have 6 fleets that have no ships, i.e., "0/17" for logistics. I can't seem to get my ships back, although they are still present in the military power graph (i.e., my military power did not sink).