Please try to install both compilers (5.6 and 5.7) on the build machine and then check.
Users with a similar issue were able to fix the issue by following the steps outlined in this SO thread. Quoting here for your convenience.
“You need to set the Build Settings > Build Options > Build Libraries for Distribution option to Yes in your framework's build settings, otherwise the swift compiler doesn't generate the neccessary
.swiftinterface
files which are the key to future compilers being able to load your old library.
This ends up in your project.pbxproj file as:
`BUILD_LIBRARY_FOR_DISTRIBUTION = YES;`
Please try the above steps and let us know how it goes.