a few people have asked why this didn't happen on the 3090ti and well apart we can't see in the inside of the cable, they are made by different companies.
The company who made the connector at the end of the cable for the RTX3090ti adaptor was Molex. The company who has made the connector on these new adaptors and cables for the RTX4090 is Amphenol and if you compare the specs you can see the two connectors are not quite the same
For example the Molex connector had a different 4mm pitch and it was rated for 10.5a of current through each pin, the new Amphenol connector has a 3mm pitch and is rated for only 9.5a of current.
So despite looking the same from the outside, they are not.