Some sysctl options like nf_conntrack_buckets are diffrent between a clean install and the first reboot of installed system
To reproduce, install a clean image, reboot the system, check the sysctl option, and reboot again.
After the reboot of loaded system, we got a different value for the net.netfilter.nf_conntrack_buckets

Before and after reboot:

vyos@vyos:~$ sysctl net.netfilter.nf_conntrack_buckets
net.netfilter.nf_conntrack_buckets = 65536
vyos@vyos:~$ 
vyos@vyos:~$ reboot now

vyos@vyos:~$ sysctl net.netfilter.nf_conntrack_buckets
net.netfilter.nf_conntrack_buckets = 32768
vyos@vyos:~$

In other cases, I saw even worse changes

# before reboot
net.netfilter.nf_conntrack_buckets = 262144

# after reboot
net.netfilter.nf_conntrack_buckets = 32768

There is no conntrack or sysctl configuration:

vyos@r14:~$ show conf com | match "sysctl|connt"
vyos@r14:~$