At elders schools/CO visits we were told that after 2 to 3 years of inactivity (that is - from the point they have gone inactive which is from SIX months AFTER their last service report was logged) we would not have to chase after "inactive ones" and could hold any evidence in abeyance until/unless they started associating again.
But ... if they are seen as disturbing any jw's or contaminating the congregation then we should take action.
So it only takes one zealot to make a fuss on what they saw on faceache or twatter and it's investigate with a view to a judicial time.
Adultery will always be investigated if there is an "innocent mate" chomping at the bit for a scriptural ground for divorce.
Xmas lights and pumpkins on the porch will usually get an investigation too if you are known as a recent x-jw in the area.
If you don't want announcing them be discreet - especially on social media!