uninitialized page in standby recovery

I built a standby with 9.4.12 and about a day later the standby crashed 
with this:

2018-02-02 16:20:44 EST,0, WARNING:  page 1347460 of relation 
base/16391/16414 is uninitialized
2018-02-02 16:20:44 EST,0, CONTEXT:  xlog redo visible: rel 
1663/16391/16414; blk 1347460
2018-02-02 16:20:44 EST,0, PANIC:  WAL contains references to invalid pages
2018-02-02 16:20:44 EST,0, CONTEXT:  xlog redo visible: rel 
1663/16391/16414; blk 1347460
2018-02-02 16:20:44 EST,0, LOG:  startup process (PID 24057) was 
terminated by signal 6: Aborted
2018-02-02 16:20:44 EST,0, LOG:  terminating any other active server 
processes

Any hints to where the corruption begins?  I don't see any disk i/o 
issues.  Not sure what to look for in the release notes,

but I'll try to patch asap, but that is difficult to get done politically.