I have written about this at the below URL as well. Tonight I have tried this again as I am using a Chain of OpenAI Assistants with different tasks and have painstakingly tested everything, a timer just in case it took time to populate the knowledge file, a random number generator to add a random number to the knowledge file filename in case multiple uploads of a file with the same filename was causing issues, for me its just completely random as to when they work properly and when they dont.
If you are just running a single Assistant, maybe you will have some luck with the original solution in this thread (It is no longer marked as solution, but its written by me)