The engineer that can solve this problem will allow top speeds in the range of 400/500 kph on /existing/ TGV tracks. Much better problem to solve than hacking a lame hyperloop.
How is this problem solved in China?
https://youtu.be/_ZZMViMDjto at 16:40 explains the problem. It's in french, but you can get the gist visually as it's a for-kids documentary.
Tldr is a wave on the cable is created at high speed, making it impossible for the train to stay in contact with the cable. The documentary also touches on another top speed limitation: how agressive the turn angles are, limiting the top speed.
The linked wikipedia article also lists speeds of Chinese non-maglev trains.
(I don't fully believe GP's comment of "The engineer that can solve this problem will allow top speeds in the range of 400/500 kph on /existing/ TGV tracks.", as narrow turns is probably a bigger contraint than the pantograph problem. Maybe a few of the more straight lines can benefit, but there's more constraints to solve before taking turns at 400/500 kph!)