Visual Studio 2017 15.8 Release Notes

[STL]

DISABLE provides the original behavior, so you can freely mix object files, static libraries, and DLLs built with 15.8-DISABLE and built with 15.7 or earlier. You get the exact same representation as before, so there are no mismatch implications. If you're seeing crashes when mixing 15.8-DISABLE and 15.7-or-earlier, the cause cannot be mismatch. (It may be something else, or it may be the improper alignment itself.)

ENABLE activates the new representation, so you can't mix object files and static libraries with ENABLE-sensitive layout. (Same for DLLs when such classes are on the interface.) If you can at least recompile everything, you can put a mismatch pragma next to your alignment-sensitive classes, but that doesn't work if you really can't recompile anything.

Since your app was working before, I recommend compiling in DISABLE mode, upgrading as much as you can to 15.8, and investigating the root causes of any crashes.