"it reserved 'the right to make substantive and relevant changes' "
And that, right there, is the seed of doom for the project.
If you don't know by now what you need from your ERP, then your project is doomed from the start.
You cannot implement any IT project, make "substantive" changes mid-way through, and expect the end result to work.
What you should do is exhaustively list your needs, the results you expect to be able to work, and get an expert to draw up the specifications that answer those needs. When you have a working platform, then you analyze what changes you require and request their implementation.
The best project manager I ever had the privilege of meeting was adamant on one point : when there was a meeting to discuss project progress, it was out of the question to add new points to the requirements list. If there were more requirements, he automatically and authoritatively shunted them to version X+1.
Because he wanted something that worked first. Then you add the bells and whistles.
It helped that he was IT manager and no-one had any authority to complain, but still.