Bingo.
One theory is that rather than linear FTL acceleration being achieved, spacetime is warped so that distant co-ordinates are continuously brought closer.
Experiments are difficult because of the start-finish conundrum. A sensor array needs to know when a particle starts its journey and when it finishes so that its velocity can be calculated.
Elaborate . . .
A warp field just curves space between two points so that a spaceship takes the shortcut of a straight line between them.
The spaceship doesn’t go any faster, it just traverses a shorter distance and arrives faster..
Light would be doing the same thing in a warp field, thus wouldn’t go faster.
I would bet we can never generate the kind of power it would take to massively bend space over large distances such as even a one light year distance - thus FTL travel will remain in the realm of Star Trek sci fi, IMO.
Shalom Aleichem