The Apple IIc Plus manual, page 110, states, ( The Apple IIc Memory Expansion Card is not designed to be used with the Apple IIc Plus. Ask your authorized Apple dealer to recommend a compatible card.)
The design of the Apple IIc Plus renders the Apple Memory Expansion Card unstable, because of timing problems associated with the gate array.
Use of the Apple IIc Memory Expansion Card in an Apple IIc+ is not supported by Apple.