Installed kernel 4.18 on my Ubuntu recently, since then snap packages broke with the following error.
It has something to do with the AppArmor exception rule for ptrace for what I could gather.
danesh@hades:$ spotify cannot perform readlinkat() on the mount namespace file descriptor of the init process: Permission denied
The workaround for now is to upgrade your snap core to the beta channel.
danesh@hades:~/kernel$ sudo snap refresh --channel=beta core