The conversions I uploaded via v201603 API don't show up in my AdWords account. There are no errors in the request log:
[Apr 06 2016 03:33:16.000000 - INFO] effectiveUser=[....] service=OfflineConversionFeedService method=mutate operators={ADD: 92} responseTime=212 requestId=00052fce7d5d40280abf3f109f0fa18e operations=92 units= server=
adwords.google.com isFault=false faultMessage=null
There's another strange case I found so far with the offline conversions upload:
I had conversion action named "Offline" and uploaded several offline conversions successfully. After this I have deleted it and created new conversion action with the same name - "Offline". The newly uploaded conversions to the newly created conversion action didn't appear even if there were no errors in the soap log and the request log. I had to rename this new conversion action to something else before this worked. It seems there's some glitch when two conversion actions has the same, even if the first one is deleted.
Now no newly uploaded offline conversions appear in my account, no matter what is the name of my conversion actions.