Can you suggest some words which can describe a person who is starting to get careless and who slacks, or the very action of becoming careless? A person who was efficiently and elaborately doing their job but with time started to be careless and their performance started to deteriorate.
marked by self-satisfaction especially when accompanied by unawareness of actual dangers or deficiencies
: marked by complacency
- The strong economy has made people complacent.
- We have grown too complacent over the years.
- We can't afford to be complacent about illiteracy.
The person in your question would have become complacent in their job.
When Susan first started, she did her job admirably, but she has recently become complacent and it's starting to show.
If you are looking for a noun, slacker might fit the bill:
A person who avoids work or effort.