3.3.0 Beta is still creating orphan fleets when using the reinforce button during a war.
No idea of the cause, but it doesn't seem very hard to reproduce, just play with big corvette swarms, click the reinforce button after each engagement, and in the meantime continue fighting with the survivors.
The orphaned fleets (usually single ships, but sometimes pairs) will accumulate at the shipyard that built them, and show as having no orders.
These orphans are forgotten by the fleet that ordered them, allowing further reinforce clicks on said fleet to create yet more ships.