Assuming a texture or file was mismatched for the host and client, validating the files having done nothing, a full uninstall, followed by a fresh install for both players has fixed the issue. Most probably, leftover files from either A17 (where the host updated from) and/or A19 (where the client updated from) were the problem. My apologies for posting this in A20 bugs when it was more a troubleshooting problem.