Notably, the example given by GP also cannot function as a restrictive clause, since "that" is acting as a demonstrative rather than the head of a clause: *Upo

Notably, the example given by GP also cannot function as a restrictive clause, since "that" is acting as a demonstrative rather than the head of a clause: *Upon the submission of the cause the appellant made a motion (to amend its assignments of error) that motion is now granted. The current ungrammaticality of the original example given in OP is due to the presence of "motion" within the wh-phrase (c.f., "Which motion is now granted?"), which does not have an equivalent construct for restrictive clauses using "that".