The option names have changed, and the configuration was not adapted. Please run:
ucr set \
ox/cfg/mailfilter.properties/com.openexchange.mail.filter.loginType="$(ucr get ox/cfg/mailfilter.properties/SIEVE_LOGIN_TYPE)" \
ox/cfg/mailfilter.properties/com.openexchange.mail.filter.credentialSource="$(ucr get ox/cfg/mailfilter.properties/SIEVE_CREDSRC)" \
ox/cfg/mailfilter.properties/com.openexchange.mail.filter.port="$(ucr get ox/cfg/mailfilter.properties/SIEVE_PORT)"
systemctl restart open-xchange.service