UPDATE: September 11, 2019:
For reasons unknown, Intel has pulled the original Product Change Notification (PCN). The company has now informed clients that it will continue shipping Apollo Lake CPUs with the B1 stepping. The F1 stepping will be offered to clients that require "Long Life Product Availability". The new PCN claims the B1 stepping chips do meet all Intel quality goals for PC usage.
Intel issued a Product Change Notification (PCN) to inform its partners that it's rolling out a new stepping for its 14nm Apollo Lake processors. Apparently, there are issue with the Low Pin Count (LPC), Real Time Clock (RTC), and SD Card interfaces on the Apollo Lake CPUs. This includes the Intel Celeron N3350, J3355, J3455 processors and Intel Pentium N4200 processor.
These four chips suffer from a level of signal degradation for these interfaces at a rate higher than what Intel's quality goals dictate. Basically, users of these chips may see their device malfunction earlier than expected.
The Apollo Lake B1 stepping is phased out and is replaced by the new F1 stepping. The new parts will receive an "E" suffix and will be marketed as Celeron J3455E, J3355E, N3350E and Pentium N4200E.
Tom's Hardware reports the LPC bus degradation issues are the ame as those seen on the Atom C2000 and E3800 family. The Apollo Lake processors are primarily used in low-end desktop, laptop, 2-in-1, and All-in-One computers.
If you own a device with one of these chips it seems there's not much you can expect once the warranty period is over.