Transports.Websocket is not terminate

[yangukmo]

I'm making an app that repeats connect/terminate multiple times without closing the app.
And the number of processes increased for unknown reasons.
As a result of checking the log, webclient_socket is not normally terminated.

# process count: 0
{:ok, socket} = Socket.start_link(socket_config)

wait_for_socket(socket)
# process count: 4
{:ok, channel} = Channel.join(socket, "user-1234")
# process count: 5
Channel.stop(channel)
# process count: 4
Socket.stop(socket)
# process count: 3

# Repeat
{:ok, socket} = Socket.start_link(socket_config)

wait_for_socket(socket)
# process count: 7
{:ok, channel} = Channel.join(socket, "user-1234")
# process count: 8
Channel.stop(channel)
# process count: 7
Socket.stop(socket)
# process count: 6

...

As a result, processes accumulate and the app is terminated.
How can I shutdown a websocket completely?