Couchbase (4 nodes on AWS Ubuntu instances);
4.1.0-5005 Enterprise Edition (build-5005).
Nothing at all in the logs - like I said all the other apps run fine and have not had this problem - I really think it’s on the app side. I can still upload them all to support but I doubt it’s relevant.
C# App:
AWSSDK 2.3.52.0
Running on windows
The logs on the app were set to writing -error level logs- to a file, and all the rest just to the logviewer which for reasons beyond me was paused 
So all I have for the incident is the following every 5 seconds over a few hours (because we keep trying the operation if for some reason the app fails to get through):
2016-07-04 14:49:35.3771 AppSync.<Start>b__3 => AppSync.DoPeriodicSync => AppLog.Error Error Uncaught exception - ServiceNotSupportedException
The cluster does not support Data services.
at Couchbase.Core.Buckets.CouchbaseRequestExecuter.SendWithRetry[T](IOperation`1 operation)
at Couchbase.CouchbaseBucket.Get[T](String key)
at [...]
Obviously I’m running the viewer now, but I can’t provide the logs until it happens again 
UPDATE (And updated the title)::
So there is actually not much more in the logs
-Ridiculously often the on going connection with couchbase is lost while it’s idle (kind of normal) so it reconnects before doing an operation; Eventually that re-connection leads to the error above.
2016-07-08 14:05:14.2050|INFO|Found 1 operation requests.
2016-07-08 14:05:14.2050|INFO|Processing operation request ID 37414.
2016-07-08 14:05:14.2050|INFO|Is OBJECT operation request
2016-07-08 14:05:14.2050|INFO|Connection with couchbase lost trying to reset connection.
2016-07-08 14:05:14.2050|INFO|Closing connection to bucket
2016-07-08 14:05:14.2050|INFO|Opening connection to bucket
2016-07-08 14:05:15.5930|INFO|Deleted processed operation request 37414
vs
2016-07-08 14:12:41.3990|INFO|Found 1 operation requests.
2016-07-08 14:12:41.3990|INFO|Processing operation request ID 37416.
2016-07-08 14:12:41.3990|INFO|Is OBJECT operation request
2016-07-08 14:12:41.3990|INFO|Connection with couchbase lost trying to reset connection.
2016-07-08 14:12:41.3990|INFO|Closing connection to bucket
2016-07-08 14:12:41.3990|INFO|Opening connection to bucket
2016-07-08 14:12:43.2560|ERROR|Uncaught exception - ServiceNotSupportedException
The cluster does not support Data services.
at Couchbase.Core.Buckets.CouchbaseRequestExecuter.SendWithRetry[T](IOperation`1 operation)
at Couchbase.CouchbaseBucket.Get[T](String key) [...]
2016-07-08 14:12:43.2560|INFO|Going to sleep for 5 seconds.
2016-07-08 14:12:48.2790|INFO|Found 1 operation requests.
2016-07-08 14:12:48.2790|INFO|Processing operation request ID 37416.
2016-07-08 14:12:48.2790|INFO|Is OBJECT operation request
2016-07-08 14:12:48.2790|ERROR|Uncaught exception - ServiceNotSupportedException
The cluster does not support Data services.
at Couchbase.Core.Buckets.CouchbaseRequestExecuter.SendWithRetry[T](IOperation`1 operation)
at Couchbase.CouchbaseBucket.Get[T](String key) [...]
I feel like we can manage that error and force the connection closed to then re-open it - but I still totally stumped as to what could cause this. I guess the next step is to upload the couchbase logs to support even though there doesn’t seem to be anything in them… unless I’m missing something.
Could it be possible that while other processes we have (on other machines) constantly communicate with couchbase they do not encounter this, while here we regularly lose the connection while idling and eventually get the error?