beast: Assertion failed: (bytes_transferred > 0)

My program often crashes with the following beast assertion:

Assertion failed: (bytes_transferred > 0), function operator(), file xxxx/include/boost/beast/websocket/impl/read.ipp, line 436.

Version of Beast

120

All relevant compiler information

$ gcc --version
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 8.0.0 (clang-800.0.42.1)
Target: x86_64-apple-darwin16.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin