Try to send a test webhook from Stripe Dashboard.
Make sure you have debugging enabled on Stripe Payments settings.
Go to https://dashboard.stripe.com/test/webhooks/, click on https://example.com/?asp_hook=test and click Send test webhook... button. Select customer.subscription.updated from the dropdown and click Send test webhook.
Then go to Stripe Payments settings page and click “View Log”. You should see similar lines at the bottom of the log:
[08/24/2020 5:53:05 PM] – [Sub] Processing “customer.subscription.updated” hook.
[08/24/2020 5:53:05 PM] – [Sub] Searching for subscription sub_00000000000000
[08/24/2020 5:53:05 PM] – [Sub] FAILURE: Subscription not found. Aborting.
Let me know if those are there.