Not sure you already solved this problem, but it is good to share my solution on this.
I got same problem on BPC 10.1 on HANA with Excel 2013, and solved.
1. AFTER_REFRESH was the main problem. I've changed the name just like AFTER_REFRESH_M and call it. Then the problem was gone. You should save the template and close excel, then rerun excel and open the template. Once the problem happened, looks like there is memory problem in excel so you should restart Excel from the scratch.
2. Not sure you code Calculation Mode for AFTER_REFRESH or WORKBOOK_OPEN event, it also looks like memory relationship with FPMClient Library, so carefull to use Calculation Mode, once you have the symptom and save wrong template, you might not get into right course to solve the problem. Therefore you need to snapshot working version whenever you change something. EnableEvents is also related.
Best Regards,
YH Seo