Apple has accused Qualcomm of double-dipping on patent royalties, charging both when Apple licensed the patent portfolio and again when it sold cellular chipsets. Qualcomm, meanwhile, has maintained that its patents venture beyond chipsets and that its licensing approach has been valid. It has gone so far as to threaten to block iPhone X sales, although that's purely symbolic now that the phone has been discontinued.
The timing raises the potential for another lengthy patent battle similar to the seven-year conflict between Apple and Samsung. However, Apple may have an ally on its side. The FTC is set to go to trial against Qualcomm over antitrust issues on January 4th, and the eventual outcome of that case might influence the chip designer's chances against Apple. If the FTC prevails, Qualcomm might have trouble convincing the San Diego court that its royalty practices are fair.