Swift compiler error - Uknown type name XSym from file EILIndoorSDK.h

When I try to compile some code one of my coworkers have written Swift gives me the following compiler errors (relating to EILIndoorSDK.h)

Contents of the EILIndoorSDK.h file:

  1. XSym <- Uknown type name ‘Xsym’
  2. 0075 <- Expected identifier or ‘(’
  3. A string of letters and numbers
  4. …/…/…/EstimoteIndoorSDK/EstimoteIndoorLocationSDK/Headers/EILIndoorSDK.h

Apparently, this app has worked fine to deploy before (the app was created in july of 2017), but now it gives me that error. I’ve tried using Xcode 8 and Xcode 9.

Other error:

Failed to emit precompiled header ‘[omitted]’

What have I been doing wrong?