This problem we have seen before, and I think it was a luatex bug then. Which luatex is this ? 0.60.1 ?
It was .50, so I updated to .60. I'm still getting errors with the same behavior, e.g.: % block of text block of text and block of text % block of text work, but block of text block of text doesn't. The difference is that now they are reporting differently: " ! Undefined control sequence. <argument> \@@bklocation \processaction ...-> \expandaction \!!stringa{#1 } \ifx \!!stringa \empty \l..." In addition, everything involving inferiors, superiors, numerators and denominators is now broken. For example: \definefontfeature[in][body][sinf=yes]%inferior Cs{\setff{in}133} has no effect.
Also, debugging this really needs a complete test input file.
I don't know how to make one.