I have experienced this too!
After six consecutive Libre sensors without experiencing a problem I had exactly the same symptoms that you describe. I assumed it was a one-off problem, and tried another sensor on the same arm. After about 5 days the same symptoms developed again - itch, ooze, pain!
I tried another sensor on the other arm, working on the theory that maybe it was a site issue, and the same thing happened there. So it would appear that I've developed an allergic reaction to the adhesive.
The rash was very painful, raw red and "oozing". This was about 3 months ago, and I've followed up with Abbott DC. They say that the adhesive type hasn't been changed so it is an allergy (they're also refunding the three sensors).
This seems to be a problem that others have had:
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(17)32142-6/fulltext
I was finding the Libre very useful indeed (I'm just a T2), so I'm keen to hear if anyone else who has experienced this has found a reliable method of attaching the sensors without suffering a reaction, please? ADC's advice is "talk to a healthcare professional" !