IntelliJ "Debug info unavailable"

I have a Java Tomcat web application built in IntelliJ that calls code in another module called "Stuff". I've attached the source of the relevant code to "Stuff" so I can step into it and hit breakpoints, but I cannot see variables or their values. Watches don't work either. All I get is "Debug info unavailable".

How do I see the debug info?

Why my debugger is not working in IntelliJ?

If the code is outdated, or the versions (the source code and the compiled class) mismatch in any way, it can happen that the debugged is giving the IDE information to show a certain line, but that information is not correct giving the current source code, which might cause what appears to be the debugged "jumping" ...

How do I enable debugging in IntelliJ?

Run the program in debug modeClick the Run icon in the gutter, then select Modify Run Configuration. Enter arguments in the Program arguments field. Click the Run button near the main method. From the menu, select Debug.

How do I get out of debug mode in IntelliJ?

Terminate a debugger sessionClick the Stop button in the Debug tool window. Alternatively, press Ctrl+F2 and select the process to terminate (if there are two or more of them).

Please compile using the following options: