From the changelog:

"6.0.0
Breaking change - R.map/R.filter/R.reject/R.forEach/R.partition doesn't pass index as second argument to the predicate, when looping over arrays. The old behaviour of map, filter and forEach can be found in Rambdax methods R.mapIndexed, R.filterIndexed and R.forEachIndexed(introduced in version 6.1.0)."

But rejectIndexed was not added together with the others (and not partitionIndexed either?).

Also, the rejectIndexed REPL is broken.