Plugin replaces old pretty links and creates multiple similar entries

Something strange is happening when I try to add some specific links.

For example, when I add https://aviasales.tp.st/jSrk9tjC, the plugin creates a pretty link for it, no problem.
I.e. it would be https://domain.com/korea1

But when I go on and add another link https://aviasales.tp.st/pstgEpHI with a different slug (i.e. https://domain.com/korea2), the plugin does not only do this, but also REPLACES target link, title and slug for the PREVIOUSLY pretty link as well.

So in this case I get two entries for https://domain.com/korea2 leading to https://aviasales.tp.st/pstgEpHI

I mean, I get two absolutely similar pretty links, and the information from the first entry lost.

If I go on and continue adding DIFFERENT links from the same affiliate system, this continues (so I get more and more similar links that are all copies from the last entry). Like, I mean, I can get 5 or 10 identical links instead of different ones, as if they all point to the same line in the database.

Similar effect is happening with my efforts to add links like https://tripster.tp.st/vlTaozT2.

At first this effect seemed to be the case with specific links only, and plugin worked fine for other links. But now I tried to add a pretty link for https://ign.com, and the effect was the same. ??