vagrant reload lost synced folder

Question

I have read several exactly same questions here, but still can not solve my problem. So I ask here again, hope someone can help:

Windows 10 host, Ubuntu 2020.04 guest

Once I run "vagrant reload", the sync folder got lost in the guest. Same as I reboot, sf also got lost

And here is config.yaml file

vagrantfile:
target: local
vm:
    provider:
        local:
            box: bento/ubuntu-20.04
            box_url: 'false'
            box_version: '0'
            chosen_virtualizer: virtualbox
            virtualizers:
                virtualbox:
                    modifyvm:
                        natdnshostresolver1: false
                    showgui: 0
                vmware:
                    numvcpus: 1
                parallels:
                    linked_clone: 0
                    check_guest_tools: 0
                    update_guest_tools: 0
            machines:
                machine1:
                    id: moon
                    hostname: moon
                    network:
                        private_network: 192.168.10.10
                        forwarded_port:
                            port1:
                                host: '8510'
                                guest: '22'
                    memory: '1536'
                    cpus: '1'
    provision:
        puppet:
            manifests_path: puphpet/puppet/manifests
            module_path:
                - puphpet/puppet/modules
                - puphpet/puppet/manifests
            options:
                - '--verbose'
                - '--hiera_config /opt/puphpet/puppet/hiera.yaml'
    synced_folder:
        folder1:
            owner: vagrant
            group: vagrant
            source: ./
            target: /var/www
            sync_type: default
            smb:
                smb_host: ''
                smb_username: sidu
                smb_password: ''
                mount_options:
                    dir_mode: '0775'
                    file_mode: '0664'
            rsync:
                args:
                    - '--verbose'
                    - '--archive'
                    - '-z'
                exclude:
                    - .vagrant/
                    - .git/
                auto: 'true'
    usable_port_range:
        start: 10200
        stop: 10500

Update #1

After so much pain, I now figured out how to fix. By downloading the latest Vagrant, the shared folders is back

Further thinking: it might be the reason that old vagrant does not support OpenSSH key

Update #2

After restart PC / OR / vagrant reload many times, works, BUT it lost again after many times later.

Thus found this: Vagrant was unable to mount VirtualBox shared folders

Now currently working as:

by nottherealironman

vagrant plugin install vagrant-vbguest
vagrant vbguest --status
vagrant ssh
sudo apt-get install virtualbox-guest-x11
exit
vagrant vbguest --do install
vagrant reload

Now everything back to normal, i will keep this updated after more testing later

Several days later confirmed above #2 works