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