Comment 9 for bug 1877161

More information,

This has been introduced in 2.6.0
before that two different matrix-element/directory were created but only one was created starting with 2.6.0 (but with this issue in the process definition of the second process)

The issue is related to the function
reorder_process
which has wrong size input for the two permutation element.
Those input are given by:
amplitude_tag[-1][0].get_external_numbers()

so the issue is either in the definition of the tag and/or in the get_external_numbers routine ...

Cheers,

Olivier