signmessage and verifymessage CLI commands not accepting Address from getnewaddress?
signmessage and verifymessage only work with legacy type addresses. They do not work with segwit addresses. There is ongoing work to introduce a new message signing standard that will work regardless of address type.
Some discussion about why they only work on legacy addresses can be found in this issue: https://github.com/bitcoin/bitcoin/issues/10542