WinSCP 5.17.7 on Windows 10, the SFTP server is sshd on Linux Debian Buster. When downloading files over 2 GB, the "Transferred" counter in the download queue window wraps around to 0 near 2 GB.
Not anymore. Maybe it was a case of pause and restart; I left the laptop with another person for a while (3 GB is a long download), then saw the counter being about the current file size minus 2 GB. If it was indeed a int size related bug, it'd be trivially reproducible. If it doesn't reproduce, nevermind.