Some task groups, not all, spam multiple "completed orders" messages in the Event Update window. Other message types are also affected, for example "unable to"-type messages.
I have been unable to spot any connections between the affected task groups or what sets them apart from the unaffected ones. All new ships seems to behave them selves for a while, and then some of them gets over-informative.
In the following example the "Alhambra Victory" is an old (+5 years) one-ship freighter group, while the "Cargo 8" is five-ship freighter group from the same build; here both task groups deliver 21 "completed orders" messages. The Alhambra was never a member of a multi-ship group, except before she split from the shipyard she was built in, I checked the task group history.
The "Civil Service" is a five-ship group, only a few years old, and here they deliver only three identical messages. And "Hercules" is my old tug, as old as the universe itself, 38 years. Relatively well-behaved here, only four messages, but I have seen this particular one-ship fleet do a full page of identical messages.
The "Goblin" etc. are all brand new and well-behaved.
This phenomenon builds up over time, it seems, is all I can say.
29th May 2063 16:41:21,Sol,Civil Service has completed orders
29th May 2063 17:11:21,Sol,Civil Service has completed orders
29th May 2063 17:41:21,Sol,Civil Service has completed orders
29th May 2063 17:41:21,Gliese 526,GE Francisco Pizarro is unable to set up all five of its special survey orders as there are not enough acceptable destinations within ten billion kilometers
30th May 2063 17:41:21,Gliese 526,GE Francisco Pizarro is unable to set up all five of its special survey orders as there are not enough acceptable destinations within ten billion kilometers
1st June 2063 10:11:21,Gliese 526,GE Francisco Pizarro is unable to set up all five of its special survey orders as there are not enough acceptable destinations within ten billion kilometers
2nd June 2063 12:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 12:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 13:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 13:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 13:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 13:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 14:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 14:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 14:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 14:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 15:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 15:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 15:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 15:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 16:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 16:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 16:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 16:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 17:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 17:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 17:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 17:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 18:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 18:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 18:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 18:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 19:11:21,Kyrene,TG Atlas has completed orders
2nd June 2063 19:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 19:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 19:11:21,Kyrene,TG Atlas has carried out orders to detach any tractored ships
2nd June 2063 19:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 19:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 19:41:21,Kyrene,TG Atlas has completed orders
2nd June 2063 20:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 20:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 20:11:21,Kyrene,TG Atlas has completed orders
2nd June 2063 20:41:21,Kyrene,TG Atlas has completed orders
2nd June 2063 20:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 20:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 21:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 21:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 21:11:21,Kyrene,TG Atlas has completed orders
2nd June 2063 21:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 21:41:21,Kyrene,TG Atlas has completed orders
2nd June 2063 21:41:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 22:11:21,Kyrene,TG Atlas has completed orders
2nd June 2063 22:11:21,Sol,Cargo 8 has completed orders
2nd June 2063 22:11:21,Sol,FT Alhambra Victory has completed orders
2nd June 2063 22:41:21,Kyrene,TG Atlas has completed orders
2nd June 2063 22:41:21,Sol,Cargo 8 has completed orders
2nd June 2063 22:41:21,Sol,FT Alhambra Victory has completed orders
3rd June 2063 11:41:21,Sol,Cargo TG 1 has completed orders
4th June 2063 10:41:21,Kyrene,TG Hercules has completed orders
4th June 2063 10:41:21,Kyrene,TG Hercules has carried out orders to detach any tractored ships
4th June 2063 11:11:21,Kyrene,TG Hercules has completed orders
4th June 2063 11:41:21,Kyrene,TG Hercules has completed orders
4th June 2063 11:41:21,Unknown,Perry Transport and Trading has scrapped Perry Small F4 409 (Perry Small F4 class) due to its replacement by a newer vessel
4th June 2063 11:41:21,Sol,Perry Transport and Trading has launched a new Perry Small F5 class Freighter
4th June 2063 11:41:21,Unknown,The Morale of 67th Marine Battalion has increased to 109
4th June 2063 11:41:21,Sirius,The Katherine Noble Geology Team has completed its surface-based geological survey of Sirius-A Asteroid #67
4th June 2063 11:41:21,Sol,The crew of Ballista has completed shore leave and is fully rested
4th June 2063 11:41:21,Sol,The crew of Arbalest has completed shore leave and is fully rested
4th June 2063 11:41:21,Sol,The crew of Gandalf has completed shore leave and is fully rested
4th June 2063 11:41:21,Kyrene,The crew of Hercules has completed shore leave and is fully rested
4th June 2063 11:41:21,Sol,The crew of Arrow has completed shore leave and is fully rested
4th June 2063 11:41:21,Sol,The crew of Swale has completed shore leave and is fully rested
4th June 2063 11:41:21,Sol,The crew of Goblin has completed shore leave and is fully rested
5th June 2063 05:41:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 06:11:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 06:41:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 07:11:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 07:41:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 08:11:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 08:41:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 09:11:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 09:41:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 10:11:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 10:41:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 11:11:21,Gliese 526,GE Francisco Pizarro has completed orders
5th June 2063 11:41:21,Gliese 526,GE Francisco Pizarro has completed orders