After update I can't run arc because of "Failed to load class or interface 'PhutilClassMapQuery'"

Looks like arc upgrade failed to work properly, leaving you in an inconsistent state.

Assuming you installed arc using the instructions from https://secure.phabricator.com/book/phabricator/article/arcanist_quick_start/ :

run git fetch; git reset --hard origin/master in each of somewhere\libphutil and somewhere\arcanist. That will reset your arcanist install to the latest version.