In situations like T145878 it would be nice to be able to poke into the live python code of the affected process to figure out what's going on or at least find out which thumbnail url was requested.
I've given gdb attaching to a live process a first try on deployment-imagescaler01 and it doesn't seem to work properly, complaining that it's "Unable to locate python frame" when I ask for py-locals. I couldn't find a solution to that problem. I wonder if it needs more debugging symbols than what's currently installed on deployment-imagescaler01
An alternative seems to be to pre-wire thumbor with a signal handler: http://blog.devork.be/2009/07/how-to-bring-running-python-program.html this might be better as it would run the actual python debugger, which might be a better tool for the task than gdb.
Anyway, this requires investigation and experimentation as it wasn't immediately obvious what the best approach was when looking into T145878