I am not sure why this is happening in your case. Would you please kindly update the theme to version 5.2.4 and the Cornerstone to version 2.1.6. The new version does have better error reports and you may find that there is an error of some kind happening in the environment.
I suggest that you go through a typical troubleshooting process explained here:
Kindly get back with the result of the tests you have done.