A large number of customers are reporting an identical bug where they're unable to log into their tool. You're unable to replicate this. What are you going to do next?

Firstly, try with an alternate user profile to see if it helps. Next we can try to get a network trace, system trace and logs if that helps. If that doesn't, then try with a debug build to see if that can capture any meaningful logs.

First I will try to islotae the problem. Is the login issue happening only for customers in a specific geography/location, specific platform - web, android, iOS or any other demographic - recent sign ups or old customers etc.

Once I identify a cohort that should give some indication on any internal/external factors that may be causing this:

Have we seen this issue before in the last days/weeks/months

Any new features launched which could be impacting this

Any deployment issues

Any service avalability issues

External dependencies - browser, firewall etc.

If I am not able to reproduce the issue, will ask customer to reproduce the issue and share the logs. Will also provide instructions to collect the logs. If the customer is not able to reproduce the issue, I will ask customer to share details which will help me identify the activity on myside and diagnose the issue.