Not easily reproducable, unfortunately. It usually happens after a few days of DO being open, and many file transfer sessions from SFTP to the local machine. All of a sudden, at the beginning of a new transfer, the "Copying" window will get stuck on the "counting files" step.
The more serious problem is that when it gets stuck, the Copying window also does NOT allow you to cancel the stuck operation. The "Abort" button does not work. You can pause the transfer (and then resume it), but it remains stuck. The only way to interrupt the stuck transfer is to kill the dopus.exe process. This is a bug- DO should always allow you to abort a stuck transfer.
Looking at the FTP log, it's pretty normal until it just ends:
Opening Connection XXX:22
Server version: SSH-2.0-OpenSSH_9.0p1-hpn15v2
Using SSH protocol version 2
We claim version: SSH-2.0-PuTTY_Directory_Opus
Server supports delayed compression; will try this later
Doing ECDH key exchange with curve Curve25519 and hash SHA-256
Server also has ecdsa-sha2-nistp521 host key, but we don't know it
Host key fingerprint is:
XXXXX
Initialised AES-256 SDCTR client->server encryption
Initialised HMAC-SHA-256 client->server MAC algorithm
Initialised AES-256 SDCTR server->client encryption
Initialised HMAC-SHA-256 server->client MAC algorithm
Using username "XXXX".
Sent password
Access granted
Initiating key re-exchange (enabling delayed compression)
Opening session as main channel
Server supports delayed compression; will try this later
Doing ECDH key exchange with curve Curve25519 and hash SHA-256
Initialised AES-256 SDCTR client->server encryption
Initialised HMAC-SHA-256 client->server MAC algorithm
Initialised zlib (RFC1950) compression
Initialised AES-256 SDCTR server->client encryption
Initialised HMAC-SHA-256 server->client MAC algorithm
Initialised zlib (RFC1950) decompression
Opened main channel
Started a shell/command
SSH: CTS CONNECTED
After about 5 minutes of being stuck, "Connection closed" appears at the end of the FTP log. Great. Except... even after the connection is closed, the Copying window remains stuck open at "counting", and Abort still does not close the window.
I can confirm that the server is garden variety modern OpenSSH, and I never had any problems with it when I connected to it through a mapped drive via SSHFS. I only experience these timeouts/stuck connections when using DO's native SFTP functionality. Pretty evident that's where the bug is.
If it is possible to enable a more verbose debug level in DO, I can turn that on and give you more detailed logs for the next time it happens.