If you have both criteria selected, the size matters only when timestamps match.
See https://winscp.net/eng/docs/ui_synchronize#criteria

You may want to try the Mirror mode:
https://winscp.net/eng/docs/task_synchronize_full#mode

On the next time, do not abort the synchronization, during temporary connectivity problems. That should allow WinSCP to resume the transfer once the connection is restored.

I'm trying to sync a local folder to NAS. problem, upload failed because of loss of network connectivity, the file was not sent completely, when I try to sync again, it does not update the file.

it is true that the file in the NAS is with a more recent date, but as the size is different it should upload the file

code:
synchronizationResult =
session.SynchronizeDirectories(
SynchronizationMode.Remote, @"d:\12ch",

"/DESENVOLVIMENTO/Teste", false,false,SynchronizationCriteria.Either);
LOGS:

type=cdir;sizd=4096;modify=20171020180125;UNIX.mode=0777;UNIX.uid=1001;UNIX.gid=1000;unique=901g16846ee; .
. 2017-10-21 15:53:37.263 type=dir;sizd=29;modify=20171017175125;UNIX.mode=0777;UNIX.uid=0;UNIX.gid=0;unique=100g137f; ..
. 2017-10-21 15:53:37.263 type=file;size=4130139;modify=20171020180128;UNIX.mode=0777;UNIX.uid=1001;UNIX.gid=1000;unique=901g16846ef; BLUDV.mp4
. 2017-10-21 15:53:37.263 Directory listing successful
. 2017-10-21 15:53:37.263 ..;D;0;1899-12-30T00:00:00.000Z;0;"" [0];"" [0];---------;0
. 2017-10-21 15:53:37.263 BLUDV.mp4;-;4130139;2017-10-20T18:01:28.000Z;3;"1001" [0];"1000" [0];rwxrwxrwx;1
. 2017-10-21 15:53:37.272 Remote file '/DESENVOLVIMENTO/Teste/BLUDV.mp4' [2017-10-20T18:01:28.000Z] [4130139] is modified comparing to local file 'd:\12ch\BLUDV.mp4' [2017-09-22T18:12:50.000Z] [33957794]
< 2017-10-21 15:53:37.272 Script: Nothing to synchronize.
> 2017-10-21 15:53:37.384 Script: exit
. 2017-10-21 15:53:37.384 Script: Exit code: 0
. 2017-10-21 15:53:37.391 Disconnected from server