dcc.Store callback firing multiple times

Describe your context

dash                      1.9.1               
dash-bootstrap-components 0.8.3               
dash-core-components      1.8.1               
dash-daq                  0.4.0               
dash-html-components      1.0.2               
dash-renderer             1.2.4               
dash-table                4.6.1               

- OS: MacOS 10.15.3
- Browser: Safari 
- Version 13.0.5

Describe the bug

The dcc.Storage component seems to trigger twice (sometimes more) on starting the app and sometimes on subsequent triggers. See example below.

Minimal working example code:

import dash

import dash_html_components as html
import dash_core_components as dcc
from dash.dependencies import Output, Input, State
from dash.exceptions import PreventUpdate

app = dash.Dash(__name__)

app.layout = html.Div([
    dcc.Store(id='local', storage_type='local'),
    html.Div(html.Button('localStorage', id='local-button')),
    html.Div(0, id='local-clicks'),
])


@app.callback(Output('local', 'data'),
              [Input('local-button', 'n_clicks')],
              [State('local', 'data')])
def on_click(n_clicks, data):
    if n_clicks is None:
        raise PreventUpdate

    app.logger.info(f"Updating data store")

    data = data or {'clicks': 0}

    data['clicks'] = data['clicks'] + 1
    return data


@app.callback(Output('local-clicks', 'children'),
              [Input('local', 'modified_timestamp')],
              [State('local', 'data')]
              )
def on_data(ts, data):
    if ts is None:
        raise PreventUpdate

    app.logger.info(f"New data found! ({ts}, {data})")

    return f"{ts}, {data['clicks']}"


if __name__ == '__main__':
    app.run_server(debug=True, port=8077, threaded=True)

Example output:

Running on http://127.0.0.1:8077/
Debugger PIN: 597-637-135
New data found! (1584011957193, {'clicks': 24})
New data found! (1584011957193, {'clicks': 24})
Updating data store
New data found! (1584012443177, {'clicks': 25})
New data found! (1584012443177, {'clicks': 25})
Updating data store
New data found! (1584012445159, {'clicks': 26})
New data found! (1584012445159, {'clicks': 26})

Expected behavior

The callback should fire once.

Start by running the minimal Python app and reproducing the duplicate logs from the dcc.Store callbacks, especially the modified_timestamp input. Trace the Store and callback update flow, then verify that the callback fires once on startup and once per subsequent store update.