Unable to connect worker node to kubernetes cluster

Definitely check your version of kubeadm and kubelet, make sure the same version of these packages is used along all of your nodes. Prior to installing, you should "mark and hold" your versions of these on your hosts:

check your current version of each:

kubelet --version

check kubeadm

kubeadm version

if they're different, you've got problems. You should reinstall the same version among all your nodes and allow downgrades. My versions in the command below are probably older than what is currently out, you can replace the version number with some more up to date, but this will work:

sudo apt-get install -y docker-ce=18.06.1~ce~3-0~ubuntu kubelet=1.12.2-00 kubeadm=1.12.2-00 kubectl=1.12.2-00 --allow-downgrades

then, once they're installed, mark and hold them so they can't be upgraded automatically, and break your system

sudo apt-mark hold docker-ce kubelet kubeadm kubectl