Page Blobs are primarily used by HBASE. HBASE replication, which apparently has not been used with WASB until recently, performs non-sequential reads on log files using PageBlobInputStream. There are bugs in this stream implementation which prevent skip and seek from working properly, and eventually the stream state becomes corrupt and unusable.
I believe this bug affects all releases of WASB/HADOOP. It appears to be a day-0 bug in PageBlobInputStream. There were similar bugs opened in the past (
HADOOP-15042) but the issue was not properly fixed, and no test coverage was added.