Call a meeting with your team and have each person bring their list and a computer that they can use to access the codebase. The ideal size for a team meeting like this is about six or seven people, so you might want to break things down into sub-teams.
In this meeting you want to go over the lists and get the name of a specific directory, file, class, method, or block of code to associate with each symptom.
Even if somebody says something like,
"The whole codebase has no unit tests,"
then you might say,
"Tell me about a specific time that that affected you,"
and use the response to that to narrow down what files it's most important to write unit tests for right away.
You also want to be sure that you're really getting a description of the problem, which might be something more like "It's difficult to refactor the codebase because I don't know if I'm breaking other people's modules." Then unit tests might be the solution, but you first want to narrow down specifically where the...