Try using the TempDBInfo procedure, it shows what *currently* is inside TempDB's files and who is using it most

https://github.com/aleksey-vitsko/Database-Administrator-Tools/blob/master/TempDB%20-%20TempDBInfo.sql

Procedure is not fully finished, I am going to rework the way it shows summary information, and also planning add logging capabilities

But it is still good at looking who is the current consumer (which session or task is using most) and might help you to diagnose the problem

Here what it shows for me:

[![TempDBInfo][1]][1]


  [1]: https://i.sstatic.net/WXajb.png

If you have any comments or suggestions for SP, let me know