MixMonitor: Write factory 0x8200214 was pretty quick last t

In asterisk full log many messages of

are dropped.
What can be reason of it?
According to the audiohook.c when some factories cannot merge audioframes into one, then this message is shown.

Asterisk is 1.4.19.1
CPU is Intel® Xeon® CPU X3220 @ 2.40GHz