I have controlled what you said with platform requests. It sends the rocket even when the total is 999. It is my bad that I have not looked if there is a request . Then the 999 could be just visual but does not impact the game at the end. Thanks for support and quick response !

Would you be interested if I send you a save to see if you are able to recreate the issue ?

I have noticed an issue where flying robot frames when inserted with inserters totals to 999 kg instead of 1 ton preventing rocket to send itself to platform. (please refer to screenshot)