Some days ago an l3kernel etc update was announced. It mentioned:

  - Move experimental l3luatex code out of l3kernel: this
    requires more work before inclusion in the 'stable' release

But where has the code been moved too? Unicode-math actually did use
some of the code and now breaks due to the missing \lua_now_x:n:


! Undefined control sequence.
\__lltxmath_set_mathchar:NN ...def


before unicode-math avoids the error)

Ulrike Fischer