Bug Report: Signature Specializations Challenge progress doesn't register

After defeating an infamous mercenary in a Kirac Mission quest for a T5 Poorjoy's Asylum, I took a weapon with an "of Infamy" suffix. The progress for the challenge did not register. Screenshots below.

This image shows bug report reference number 3,996,760,447:


This image shows the "of infamy" weapon claimed, while the challenge progress is still missing:

The item must have a Mercenary-Specific Modifier:

https://poedb.tw/us/Infamous_Modifiers