• Version: < 7.2
• Platform: Windows, OSX, also whatever Travis is using.
• Subsystem: Ubuntu Subsytem in windows

A change I made in the sequelize package here: https://github.com/sequelize/sequelize/pull/10091/files#diff-696825d45557dfe5b68972fd6f69587bL15 uncovered a weird problem.
When I changed this pre-es6 class to a es6 class the build would start to fail on node v6 but not on v8, I used a binary search and identified v7.2 as the culprit, this specific release contains a v8 update which likely fixes the issue.

The issue itself is that an instance check appears to fail where it shouldn't.