As suggested in the KIT, here's a bit sniffing:

I sent a request on the Function page Z10000:

wikilambda_function_call_zobject: {"Z1K1":"Z7","Z7K1":"Z10000","Z10000K1":{"Z1K1":"Z40","Z40K1":"Z41"}}

I get randomly (about 1 in 3) the following response:

{"query":{"wikilambda_function_call":{"Orchestrated":{"success":"","data":"{\"Z1K1\":\"Z22\",\"Z22K1\":\"Z23\",\"Z22K2\":{\"Z1K1\":\"Z5\",\"Z5K2\":\"Z8K4 did not contain a valid Implementation.\"}}"}}}}

or this one:

{"query":{"wikilambda_function_call":{"Orchestrated":{"success":"","data":"{\"Z1K1\":\"Z22\",\"Z22K1\":{\"Z1K1\":\"Z40\",\"Z40K1\":\"Z42\"},\"Z22K2\":\"Z23\"}"}}}}

On the composition page, I send the following request:

{"Z1K1":"Z7","Z7K1":{"Z1K1":"Z8","Z8K1":[{"Z1K1":"Z17","Z17K1":"Z40","Z17K2":"Z10000K1","Z17K3":{"Z1K1":"Z12","Z12K1":[{"Z1K1":"Z11","Z11K1":"Z1002","Z11K2":"x"}]}}],"Z8K2":"Z40","Z8K3":["Z10001","Z10002"],"Z8K4":[{"Z1K1":"Z14","Z14K1":"Z10000","Z14K2":{"Z1K1":"Z7","Z7K1":"Z802","Z802K1":{"Z1K1":"Z18","Z18K1":{"Z1K1":"Z6","Z6K1":"Z10000K1"}},"Z802K2":{"Z1K1":"Z40","Z40K1":"Z42"},"Z802K3":{"Z1K1":"Z40","Z40K1":"Z41"}}}],"Z8K5":"Z10000"},"Z10000K1":{"Z1K1":"Z40","Z40K1":"Z41"}}

and get the following answer:

{"query":{"wikilambda_function_call":{"Orchestrated":{"success":"","data":"{\"Z1K1\":\"Z22\",\"Z22K1\":{\"Z1K1\":\"Z40\",\"Z40K1\":\"Z42\"},\"Z22K2\":\"Z23\"}"}}}}

No non-deterministic behavior there.

I only see one implementation in the sample here. When I run this through the backend, I get the success with Z42 instead of an error. Can you send me the implementations, particularly the composition one? I suspect that that's the trouble.

The first screenshot above shows the implementation:

It is just a call to "if argument then false else true"

Trying it out again, I am actually not sure whether the error appears 1 out of 3 or more 2 out of 3 times. In which case it would indicate the error is not with the composition, but with the native code!

This does not happen on the implementation pages, only on the function page.

Change 753541 had a related patch set uploaded (by Cory Massaro; author: Cory Massaro):

[mediawiki/services/function-orchestrator@master] Ensure that the selected implementation is run when multiple implementations are provided.

https://gerrit.wikimedia.org/r/753541

Change 753541 merged by jenkins-bot:

[mediawiki/services/function-orchestrator@master] Ensure that the selected implementation is run when multiple implementations are provided.

https://gerrit.wikimedia.org/r/753541