I'm afraid that's valid data for a ranking field - it's a "lexorank" value defining an issue's place in a list compared with the ones around it. It's useless on its own because it really is a definition relating to another value.
There's an old joke in England about a horseman or motorist who is lost in the deepest countryside, and stops to ask for directions. He asks the local "bumpkin" for help - "how do I get to London from here?". The local's first response is "Arr, well, I wouldn't start from here if I were you". When pressed, they say "Well, turn right at the red barn".
The second answer is technically correct, but useless without the context of where the red barn might be. That's what a lexorank field on its own is - it's a direction, but without any reference to the starting point.
This means you have to think about what you actually want to do with this ranking data. If it's for comparing with other issues from the same JIRA installation, then it could be useful (if you could work out how to read and compare it). If you want it for something else, then I'm afraid it's useless to you because there's nothing to compare it with.
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