Integration suspend when staging file write loop

Hi Experts,

I have a integration with 2 loops to write file:

But evey time when it runs to the 11th ForEachSupplierSite and 19th ForEachBU. The integration will suspend and not go to the next iteration.
( From the previous 10 times loop I can tell there are 97 iterations in ForEachBU)

Then the integraton will keep 'in progress' status and no more activity stream showing.

May I know why?

Thanks in advance!

Weitao