The first one is probably a follow-up error
org.codehaus.jackson.JsonGenerationException: Can not write a field name, expecting a value
I've experienced that one when e.g. a calculated attribute microflow throws an exception.
The second error looks like a security problem.
It might help to check the client/server traffic.
So there is a loop. In the loop, I change the object (remove one association), then delete the object at the end of the loop. For some reason, this flow cause the error. Now I have workaround to not to change the object and delete it, then it works.
But i still don't have proper explanation for the issue.