A setup was created where 2 convoys (capacity 6) scheduled for 100% load from orchard (389, 766).
Load the save (https://simutrans-germany.com/files/upload/big_2_neon_-go_-pax-mail_fruits.sve), set turbo speed and watch the convoys reach the orchard in the above coordinations. Upload stop at 5 crates and at least for a game year refuse to load 1 more crate to leave. Market even if do consume fishes start loosing almost all workers. Market worked just fine before the connection by fruit line too. It seems buggy to stop service fishes because it does not have fruits. After confirmation, edit the 10 fruits line to be scheduled to 80%. The convoy will leave. Let some minutes in turbo mode pass and edit the fruit line to 100% scheduling again. Now convoys load 100% normal and the health of transportation and market is gained back.
If it turns down that the phenomenon has roots on the algorithm that controls the goods in transit, i suggest to abandon the algorithm. I will explain in another post (https://forum.simutrans.com/index.php/topic,21863.new.html#new).