MS Office 365 Readiness Report Creator error

I have a (large) Excel 2016 XLSM project, which has Option Explicit in every module and compiles and runs with no errors, with no #REF! errors when saving.

However, when I run the latest version of the MS Office 365 Readiness Report Creator it says "Congratulations! You’ve successfully created a readiness report" but says "0% have no macros, 0% Have VBA macros, 100% Couldn't analyze".

The VBA Overview tab says "Error", "Inaccessible", "Inaccessible" under the pie charts.

In the VBA Summary tab it says "Syntax error detected in VBA project" and "Inaccessible", but my project has Option Explicit in every module and compiles and runs and saves with no errors, in the same login and session on the same computer in Excel 2016.

Any ideas, please?