Precursors quest: Where is my 6th artifact?

I got a quest in my situation log where I need to investigate 6 artifacts. Unfortunately I only got 5 of them which I all investigated:

Is that a bug? Or do I need to do something for the 6th to appear on the map?

According to this Reddit it is possible to find 6 artifacts, but it is extremely hard.

Due to the way anomaly spawns, it's extremely hard to find 6 precursor artifacts (there are 12 in total and yes AI can stop you from finishing)

A "solution" to make it easier is to manipulate the gamefiles:

Go to Stellaris\common\anomalies\00_anomalies.txt
and from line
Vultaum Precursor Discoveries
to line
EVENT SPAWNED DISCOVERIES
do following:
within each anomaly = { } scope directly under
"category=???", add new "weight" or replace existing ones value,
like this:
weight = 5000
there ought to be 76 of them.

(This "solution" is also from the Reddit-post mentioned above.)