Rudder

I have a 5.0.8 server, but when I tried to install an agent 6.0 under it,it printed errors like this:

E| n/a           Common                    Process checking                             Rudder agent proccesses check is done by the rudder-agent cron job
rudder     info: Moved '/etc/cron.d/rudder-agent_1579268651_Fri_Jan_17_13_44_12_2020.cf-before-edit' to repository location '/var/rudder/modified-files/_etc_cron_d_rudder_agent_1579268651_Fri_Jan_17_13_44_12_2020_cf_before_edit'
rudder     info: Updated rendering of '/etc/cron.d/rudder-agent' from mustache template '/var/rudder/cfengine-community/inputs/common/cron/rudder-agent-community-cron'
rudder     info: Edit file '/etc/cron.d/rudder-agent'
E| compliant     Common                    CRON Daemon                                  Cron daemon status was correct
rudder     info: Executing 'no timeout' ... '/opt/rudder/bin/curl -L -k -1 -s -f --proxy '' -o "/var/rudder/cfengine-community/rudder-server-uuid.txt" https://192.168.44.2/uuid'
rudder     info: Completed execution of '/opt/rudder/bin/curl -L -k -1 -s -f --proxy '' -o "/var/rudder/cfengine-community/rudder-server-uuid.txt" https://192.168.44.2/uuid'
   error: Anomalous ending '
P' while parsing real number: 24
Platform  : linux localhost 4.9.0 1 smp debian 4.9.0 x86_64 gnulinux
   error: Anomalous ending '
P' while parsing real number: 24

After running a rudder agent check, I was able to send my inventory and accept the node on the server.
But afterwards, the node could never update itself, always printing:

root@agent:~# rudder agent update
R: *********************************************************************************
* rudder-agent could not get an updated configuration from the policy server.   *
* This can be caused by:                                                        *
*   * an agent key that has been changed                                        *
*   * if this node is not accepted or deleted node on the Rudder root server    *
*   * if this node has changed policy server without sending a new inventory    *
* Any existing configuration policy will continue to be applied without change. *
*********************************************************************************
error: Rudder agent promises could not be updated.

When looking into the verbose log server-side of cf-serverd, I find out that the node was refused due to:

rudder     info: 192.168.44.3>    access denied to STAT: /var/rudder/share/0c462a6c-596a-443d-b610-08818b1bf28a/rules/cfengine-community/rudder_promises_generated
rudder  verbose: 192.168.44.3>    REFUSAL to user='root' of request: SYNCH 1579269894 STAT /var/rudder/share/0c462a6c-596a-443d-b610-08818b1bf28a/rules/cfengine-community/rudder_promises_generated

And this one was resulting from the removal of the cfengine key from the inventory (CFENGINE_KEY field) in 6.0, when it is still used in 5.0 to define the ACLs which guard the policy file at update time.
It seems to be fixed since #15547.