Here Oliver Cowdery initially wrote causes in 𝓞, but he immediately overwrote the s with a t and then wrote the h inline. So the correction of causes to causeth is immediate, and causeth is very likely the original reading. In his editing for the 1837 edition, Joseph Smith changed causeth to causes, but this simply represents his typical (but inconsistently applied) replacement of the archaic -(e)th ending with the more modern -(e)s ending. For general discussion, see under inflectional endings in volume 3.
Summary: Restore in Alma 30:35 causeth, the immediately corrected reading in 𝓞.