TransferManager.upload is sometimes taking 10,20,30 seconds

[edubon]

We make a very simple usage of the TransferManager, the code is quite simple
Upload upload = tm.upload(putRequest); upload.waitForCompletion();

The files to upload are most of the time very small, just 9 bytes. We measure the time taken for upload and in some cases it is more than 10 seconds, which is quite unexpected for such a small file. Also the request is send by a k8s pod running in a AWS node so I guess network should be very fast between node and s3.
For example in the last 24 hours there was 200 uploads and 21 of them to around 10 seconds. so a 10%. It is strange that it is always a few milliseconds more than 10 seconds, like 10XXX milliseconds.
There is also cases in which it take 20 seconds or even 30 or 40 seconds with exactly the same behaviour 20XXX millisecond 30XXX, 40XXX.
But never for example 15 or 16 seconds.
My question is what could be the cause of this behaviour? It could be any way to improve that? 10% of errors sound like too much.
It looks to me like there is an error in a first try and it waits internally 10 second before retry. Is that possible is it configured any internal retry in the asw.sdk for the upload?