GnuTLS error -110: The TLS connection was non-properly terminated

GnuTLS error -110: The TLS connection was non-properly terminated.

That just means that the peer just closed the socket and did not do a proper TLS shutdown. Some broken clients or servers do this. Assuming that this message relates to a data transfer you can usually ignore this because the transfer was finished anyway, so no data got lost.

Using SFTP does not give this error and also using FTP in plain text(insecure) also does not.

Of course you don't get it, since SFTP is using the SSH protocol instead of TLS and plain FTP does no encryption at all, so no TLS too. And if there is no TLS involved you can not get any TLS errors.

I really do not understand this and note that the application has been running fine for years and this just suddenly happens on like 4 servers.

It might simply be that the servers changed, i.e. either they never supported FTPS (i.e. FTP with TLS, not to be confused with SFTP) before or they now switched to a broken implementation.

If you are connecting to a cPanel server then you can temporarily fix this issue by enabling "Broken Client Compatibility" in Pure-FTP settings in WHM.