Did you notice that the Atlassian Marketplace is getting unreachable from time to time?

Recently, I have encountered this problem.

Why is it happening from time to time? I believe it could affect customers.
Sorry if such a topic already exists somewhere. I didn’t find any information here.

Yes, we also noticed it.
You may check for more information the status page - https://developer.status.atlassian.com/
Atlassian publishes information about the outage and the recovery steps.
If you want to get notification you may subscribe to updates for any service that is down.