TonyE has come up with a lead which has given good results, further testing and AIWindow.dll interrogation shows that a key identifier (unit's UUID) is not being generated for new units formed when a unit within a group is split by virtue of splitting the group (F8) but is copied from the original thus two units have the same (meant to be unique) Unit UUID. If the new and original units are together again in the same group then only one will land.

In the screen shot, centre window, the data is for the selected group's units, the numbers should be unique.

 

HCE - 2024.002 - 2024-04-02
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- Chg:00000 GE When splitting a group by splitting aircraft from a single unit
                into two units (one in donating group, one in destination group)
                the destination unit would have the unique id (uuid) of the 
                donating unit making it no longer unique.  This messed up
                further processing of Harpoon Events for those units, such
                as landing.  Fixed to not overwrite the uuid generated for
                the new unit. (thanks donaldseadog and others)

TonyD will be delighted

On 4/2/2024 at 4:30 PM, donaldseadog said:

TonyD will be delighted

I am and have confirmed the  problem fixed. Will work even with saved games as long as aircrafts have not attempted landing.