Hi everyone,
It has been uncovered that due to a bug in macOS Sierra 10.12.4, EndNote libraries with PDFs that have extensive annotations have issues. This will cause the app to hang (not crash). Previous versions of macOS Sierra are not exhibiting this. Until further notice of fix/patch from Apple we recommend to use EndNote on a previous OS.
But, if EndNote is crashing on you, please call our Support team. A crash is likely caused by something else and they can walk you through remediation steps. http://endnote.com/support
Will update as we know more.
Thank you,
Meredith