Are scientific contributions of the article listed in the abstract?

In light of the example you linked, you should indeed state your contributions, but there is no need to state that these are your contributions. So instead of stating "The contribution in this paper is considering problem A using method B", you should use "We consider problem A using method B". Doing this would have easily saved 20 words in your example without changing any of the meaning. Even more importantly, the useless words are in the beginning, which is the only part of the abstract you can actually be sure that people will read.

The default assumption on a paper is that you are presenting something new and that new thing is why people should be reading your paper, which is why will be prominently mentioned in the abstract. So the default assumption when reading an abstract is that all results mentioned describe scientific contribution. There is thus no need to explicitly mention it.

There are of course things in the abstract that are not new contributions, but they are generally made obvious by phrasing. If your abstract starts with "We survey some recent results in ..." no one expects that the results mentioned afterwards are new. Or if you are (in)directly referencing using "The well known problem of ..." then no one will think you came up with the problem. But if a sentence starts with "We show that ...", then any reader will assume that you claim to be the first one to do so in this context.

The abstract is there to let you know what the article is about and entice you to read it. I would want to know what its claimed original contributions are from the start.

Personally, I like abstracts that roughly follow a 'Background and Aims, Methods, Results, Conclusions structure'. Contributions are meant to be implicitly written and I am not a fan of explicitly writing these within the abstract. This is still a personal decision and is therefore completely left to the author.