[BUG] Long callbacks triggered multiple times with concurrency

[vkolevrestec]

Describe your context

dash                      2.0.0
dash-bootstrap-components 1.0.0
dash-core-components      2.0.0
dash-html-components      2.0.0
dash-table                5.0.0

Describe the bug

The long callback acts strange, the progress bar starts loading and then goes back and forth.
It is working locally on Ubuntu 18.

Azure configuration:
Azure App Service, Ubuntu 18

Startup command:
gunicorn --bind=0.0.0.0:$PORT -w 4 --timeout 60 wsgi:app & celery --app dashboard.celery_app worker --concurrency=8 -l info

Code setup:
long_callback_manager = CeleryLongCallbackManager(celery_dash_app, cache_by=[lambda: uuid4, ])
dashapp = dash.Dash(
...,
long_callback_manager=long_callback_manager
)

Expected behavior

The snippet should work like this one , Example 4: Progress Bar.

Screenshots

[ayhteo]

I think this might also have been described in #1769 (comment), I have a similar problem when using for loops in a long_callback.

[vkolevrestec]

Thank you for referencing the main thread.
I tried to do a workaround by increasing the interval and It's still buggy.

If I increase the interval to more than the job requires I get the result directly, but I will have to wait that extra time.

I'll try this workaround by sebbegg as well, until we get a proper solution by Dash.

[vkolevrestec]

Will be fixed in #2039