This change in falignpush.h cause hosts compiled with the new SDK to fail loading plug-ins compiled with previous versions of the SDK because it the binary layout is messed up, so that calls from the host end up in different functions in the plug-in:
#pragma pack(push, 16)
#pragma pack(push, 1)
This can be reliably reproduced with Xcode 10.2.1 (10E1001) on MacOS 10.14.4 (18E226) - I have a simple test host and plug-in, and if both are build with the same SDK all is good, but if the host uses the latest SDK and the plug-in a previous one, the function pointers are off. This also happens with publicly released, actual plug-ins that use the previous SDK.
On a related note, the following lines cause a warning in Xcode:
#pragma GCC diagnostic default “-Wpragma-pack”
#pragma GCC diagnostic default “-Wunknown-warning-option”
both lines trigger: Pragma diagnostic expected ‘error’, ‘warning’, ‘ignored’, ‘fatal’, ‘push’, or ‘pop’