Network error: Software caused connection abort, File transfer failed

First, I did saw other forum post on same error. However I didn’t find a definate solution for it, and hence posting my own.

1. I am having this issue with Filezilla, when trying to use SFTP to Ubuntu 16.04 based server. I have 3-4 different ubuntu server from Digital Ocean that are causing this error.

2. I try to connect from more than one network at my end, and all give error. This doesn’t happen to my other server which are not from digital ocean. That is strange thing.

3. Suppose I try to sftp 100 files, 70-80 give this error, but 20-30 gets uploaded, that suggest there is no actual Network issue, but some policy is stopping it.

4. I see lot of user get this error when using putty, but I am able to use putty just fine, even can connect through putty for hours without break or issue. Only Filezilla file transfer is an issue.

Any help is appreciated, I do not install FTP software in my server, only install apache, git, let’s encrypt prerequesties and php there to default Ubuntu. Even has mysql on different server.