Word or phrase to describe something that previously had a use, but now has a negative impact

Something like a remnant of a system that originally had a purpose, but has since lost its purpose, to the point of having a negative impact on the current system.

Think of something like an outdated technology, that currently has a range of issues. In it's prime, it was a good choice, but now it is causing more issues than it solves.

Real world examples:

'The system contains x technology, likely a [insert word here] from when the system was first designed.'

'The human body still has a [insert word here] tailbone.' (nowadays causing more problems than it has benefits)

Solution 1:

In the second case you mentioned, the technical term is "Vestigial"

In general, you could use the term "Obsolete"

Solution 2:

https://en.wikipedia.org/wiki/Legacy_system

Legacy - In computing, a legacy system is an old method, technology, computer system, or application program, "of, relating to, or being a previous or outdated computer system,"[1] yet still in use.

https://www.gavant.com/library/what-are-the-biggest-problems-with-legacy-software/

Here are some of the problems with legacy software and the reasons why systems need to be replaced:

https://www.lexico.com/en/definition/vestigial

Vestigial - forming a very small remnant of something that was once much larger or more noticeable. "he felt a vestigial flicker of anger from last night"

Biology - (of an organ or part of the body) degenerate, rudimentary, or atrophied, having become functionless in the course of evolution. [Vestigial organs can become detrimental: appendicitis or impacted wisdom teeth, for example.]

Solution 3:

Outdated or Obsolete would fit for the first sentence.

The system contains x technology, likely an outdated/obsolete piece of equipment/software from when the system was first designed.

As @Arunkgp mentioned, "Vestigial" is the technical term, but it doesn't mean that it's presence has negative/bad impact. It means that it doesn't have any function anymore.

I'm not sure if the word you're looking for would fit both the sentences.