Can't connect via "vagrant ssh" to vagrant box created with "vagrant package" - vagrant

Question

A vagrant box which was created using "vagrant package" cannot be connected to using "vagrant ssh".
Note - I am using libvirt and QEMU, not Virtualbox.
I took a working vagrant instance and created a vagrant box using
vagrant package --output abc.box
vagrant box add abc.box --name abc
I then created an empty directory and generated the Vagrantfile using
vagrant init
I edited the Vagrantfile and set config.vm.box = "abc"
I then tried a "vagrant up", and it hangs on the SSH connection
I ran a "vagrant -ssh-config" which returns settings. I was able to use the IP and key listed there to connect to the instance.
Can anybody tell me what the correct process is for getting this kind of instance to start properly? Is it by design that the insecure access isn't preserved in the packaged box? Should I just be installing my own SSH keys and logging in using "ssh" instead of "vagrant ssh"?
I expected the "vagrant up" to complete, but it never returned the prompt. Attempts to connect to it using "vagrant ssh" from another terminal didn't work.
I turned on debugging and saw the log entries listed below.
DEBUG ssh: == Net-SSH connection debug-level log START ==
DEBUG ssh: D, [2019-09-03T18:00:51.803268 #4837] DEBUG -- net.ssh.transport.session[1ae7be8]: establishing connection to 192.168.121.230:22
D, [2019-09-03T18:00:51.804016 #4837] DEBUG -- net.ssh.transport.session[1ae7be8]: connection established
I, [2019-09-03T18:00:51.804202 #4837] INFO -- net.ssh.transport.server_version[1ae6e64]: negotiating protocol version
D, [2019-09-03T18:00:51.804260 #4837] DEBUG -- net.ssh.transport.server_version[1ae6e64]: local is `SSH-2.0-Ruby/Net::SSH_4.2.0 x86_64-linux'
D, [2019-09-03T18:00:51.814838 #4837] DEBUG -- net.ssh.transport.server_version[1ae6e64]: remote is `SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.3'
I, [2019-09-03T18:00:51.815157 #4837] INFO -- net.ssh.transport.algorithms[1adcbe4]: sending KEXINIT
D, [2019-09-03T18:00:51.815403 #4837] DEBUG -- socket[1ae792c]: queueing packet nr 0 type 20 len 1156
D, [2019-09-03T18:00:51.815504 #4837] DEBUG -- socket[1ae792c]: sent 1160 bytes
DEBUG ssh: == Net-SSH connection debug-level log END ==
INFO retryable: Retryable exception raised: #<Errno::ECONNRESET: Connection reset by peer - recvfrom(2)>
INFO ssh: Attempting to connect to SSH...
INFO ssh: - Host: 192.168.XXX.XXX
INFO ssh: - Port: 22
INFO ssh: - Username: vagrant
INFO ssh: - Password? false
INFO ssh: - Key Path: ["/home/XXXXX/.vagrant.d/insecure_private_key"]
DEBUG ssh: - connect_opts: {:auth_methods=>["none", "hostbased", "publickey"], :config=>false, :forward_agent=>false, :send_env=>false, :keys_only=>true, :verify_host_key=>false, :password=>nil, :port=>22, :timeout=>15, :user_known_hosts_file=>[], :verbose=>:debug, :encryption=>["aes128-cbc", "3des-cbc", "blowfish-cbc", "cast128-cbc", "aes192-cbc", "aes256-cbc", "rijndael-cbc#lysator.liu.se", "idea-cbc", "arcfour128", "arcfour256", "arcfour", "aes128-ctr", "aes192-ctr", "aes256-ctr", "cast128-ctr", "blowfish-ctr", "3des-ctr", "none"], :logger=>#<Logger:0x00000000034d08c0 #level=0, #progname=nil, #default_formatter=#<Logger::Formatter:0x00000000034d0848 #datetime_format=nil>, #formatter=nil, #logdev=#<Logger::LogDevice:0x00000000034d07f8 #shift_period_suffix=nil, #shift_size=nil, #shift_age=nil, #filename=nil, #dev=#<StringIO:0x00000000034d0938>, #mon_owner=nil, #mon_count=0, #mon_mutex=#<Thread::Mutex:0x00000000034d07a8>>>, :keys=>["/home/XXXXXX/.vagrant.d/insecure_private_key"]}```