Madan,
So you say "Let's say that I have a subaction step under the Standard "transmit" action that loops over "ZCOLLECTION" Collection which contains collection of "ZOBJECT".(This Object contains one "External Data Property" along with other Object properties)."
and you also say "This behavior occurs even if "ZOBJECT" doesnt have any "External data property" and some of its Child Objects say "ZCHILDOBJECT" contains an "External data property"."
From your statement, it seems the unique item here is it is under a "Transmit" Action. You have an advance transmit action.
so based on your statement above, my best guess may be tied to the location of where all the temporary storage of the files should go. From what I can remember there was a report before that the maximum number of temporary file name was maxed out and the resolution is to go to that directory (I can't remember if it is in the C drive area or some temp directory - there may be a KBA (Knoweledge Base Article) about it) and cleaning it out by deleting all these temp files. I can't remember the name of the KBA if it is tied to attach document issue. Not sure if yours is related to yours and this is why you have it locked. I am currently not at work right now but I'll try to see if I can find it when I get back after this weekend. Again, I am not sure if this is related or if this is something new tied to the "transmit" action subaction - looping over a collection with external data object.
If this will be reported to SAP support there has to be a means to sync against your backend to reproduce. Let us say my theory above is true, this means you may not see this issue in another device. Did you try reproducing in a completely different device?
Regards,
Mark Pe
SAP Platinum Support Engineer