As reported by phajdan.jr@ in https://groups.google.com/a/chromium.org/forum/?utm_medium=email&utm_source=footer#!msg/infra-dev/wwD_wQgOhhc/Qh8YbsD9BwAJ:

"I've been hitting a presubmit error on https://chromium-review.googlesource.com/c/chromium/tools/build/+/684294 :

-      "@@@STEP_LOG_LINE@no_isolated_results_exc@  File \"<...>/pythonX.X/json/decoder.py\", line 382, in raw_decode@@@",
+      "@@@STEP_LOG_LINE@no_isolated_results_exc@  File \"<...>/pythonX.X/json/decoder.py\", line 384, in raw_decode@@@",

After training recipes manually, I produced https://chromium-review.googlesource.com/c/chromium/tools/build/+/684354 which is failing in the reverse way:

-      "@@@STEP_LOG_LINE@no_isolated_results_exc@  File \"<...>/pythonX.X/json/decoder.py\", line 384, in raw_decode@@@",
+      "@@@STEP_LOG_LINE@no_isolated_results_exc@  File \"<...>/pythonX.X/json/decoder.py\", line 382, in raw_decode@@@",

It seems that different jobs run with different versions of python, and it's not enough to remove python version from the path - the line numbers, and in theory also file names, function name, and code snippet may change.

We may need to rethink how to handle tracebacks and recipe expectations (https://chromium-review.googlesource.com/c/chromium/tools/build/+/439664)."

============

I'm personally also unable to submit CLs due to the same error:
https://chromium-review.googlesource.com/c/chromium/tools/build/+/689517
https://chromium-review.googlesource.com/c/chromium/tools/build/+/689774
I originally produced these CLs on Mac, but when patching them into my Linux machine and re-training, I still don't get any diff, so the difference must be vs the presubmit host's Python.
* Mac (system) Python version:  2.7.13
* Linux (system) Python version: 2.7.6
I assume these are still used, or we wouldn't have this problem in the first place?