When I log into webapps I see this:
Here's my profile:
What has contributed to my warning being issued? How do I find out? I know this question has been asked before, but the ones I saw applied to people who had asked questions.
You have asked two questions previously.
The first question was asked on 28th October 2011 and was closed as not a real question. The second question was asked on 17th June 2014 and was closed and migrated to StackOverflow as it was about programming.
Both of these questions have now been deleted. So overall your profile doesn't look that great 2 deleted questions, no answers and you have made one up vote.
This will be why you are seeing the warning :)
More than likely, someone who shares your network has been asking poorly-received questions.
My account is in good standing. Why am I still blocked?
The ban also takes in account the IP address. If you browse from a shared computer, or from a location that gives the same IP address to many end users, it's enough that another user who was banned or triggers the ban, will affect everyone else accessing from the same location.
To help rectify this, browse from a different location.
Assuming you don't have a bunch of deleted questions, that seems the likeliest explanation.