Comment 4 for bug 1849753

As Zygmunt said, this is a current limitation with apparmor. The problem is because both node and snap-confine are differently confined by apparmor, there is a revalidation that happens when node calls itself since it invokes snap run, which invokes snap-confine which causes the revalidation (because it is differently confined). FD delegation improvements in apparmor are planned that would allow for a better experience.

A workaround could be to avoid snap run and call node from /snap/node/current/... instead of through /snap/bin/node.