Files loss during SFTP

Hi

I was using the command put files to automate transferring folder with as many as 30 thousands of files. I notice there are some difference in file size and files number after multiple run.
So i change my script to use command synchronize just recently. I have seen only 1 out of 4 tries where the files size and number of files differ.

my question is
IS there any limit of size and number of files for transferring using put command?
Or are there any other factor like timeout etc?
Does synchronize have the above limit too?
How does i make the transfer to be more stable by getting everything from the source?

There are no limits.
There's no easy explanation for your observations.
Unless you have a log file for transfer of the file that differs in size, there's no really much we can advice you here.