Whether or not that speculation may be true remains to be seen, but according to a report from Apple 3.0, it cites Rosenblatt analyst Jun Zhang as suggesting that the production cuts could be due to quality issues with the PCBs, which is why Apple might have cancelled the production boosts while they sort it out.
According to Zhang, “We believe some Printed Circuit Board (PCB) supplier shipments of HDI boards were quickly dropped this week. This may be attributable to quality issues from Skyworks PAs. We believe this potential round of iPhone XR production cuts by Apple may be attributable to the recently found PA quality issues.”
However we should note that we haven’t really heard any complaints about major issues plaguing the iPhone XR yet given that PCBs are a big deal in our electronics. It is possible that maybe there is no issue and that the PCBs simply weren’t up to Apple’s standards, but either way since Apple will no longer announce how many units they sell, we suppose we’ll never really know for sure how well (or how badly) the iPhone XR has done for itself.