It looks like this bug:
https://winscp.net/tracker/1837

Please try to upgrade to 5.17.3.

Trying to do a GUI connect to a Solarwinds SCP server from a Windows 10 1909 system. Results in:

. 2020-04-01 09:08:49.978 --------------------------------------------------------------------------
. 2020-04-01 09:08:49.978 WinSCP Version 5.17.2 (Build 10278) (OS 10.0.18363 - Windows 10 Enterprise)
. 2020-04-01 09:08:49.978 Configuration: HKCU\Software\Martin Prikryl\WinSCP 2\
. 2020-04-01 09:08:49.979 Log level: Normal
. 2020-04-01 09:08:49.979 Local account: ******
. 2020-04-01 09:08:49.979 Working directory: C:\Program Files (x86)\WinSCP
. 2020-04-01 09:08:49.979 Process ID: 10192
. 2020-04-01 09:08:49.979 Command-line: "C:\Program Files (x86)\WinSCP\WinSCP.exe"
. 2020-04-01 09:08:49.980 Time zone: Current: GMT+2, Standard: GMT+1 (W. Europe Standard Time), DST: GMT+2 (W. Europe Daylight Time), DST Start: 29-3-2020, DST End: 25-10-2020
. 2020-04-01 09:08:49.980 Login time: woensdag 1 april 2020 09:08:49
. 2020-04-01 09:08:49.980 --------------------------------------------------------------------------
. 2020-04-01 09:08:49.980 Session name: ******@******* (Site)
. 2020-04-01 09:08:49.980 Host name: ***** (Port: 22)
. 2020-04-01 09:08:49.980 User name: ****** (Password: No, Key file: No, Passphrase: No)
. 2020-04-01 09:08:49.980 Tunnel: No
. 2020-04-01 09:08:49.980 Transfer Protocol: SCP
. 2020-04-01 09:08:49.980 Ping type: Off, Ping interval: 30 sec; Timeout: 15 sec
. 2020-04-01 09:08:49.980 Disable Nagle: No
. 2020-04-01 09:08:49.980 Proxy: None
. 2020-04-01 09:08:49.980 Send buffer: 262144
. 2020-04-01 09:08:49.980 SSH protocol version: 2; Compression: No
. 2020-04-01 09:08:49.980 Bypass authentication: No
. 2020-04-01 09:08:49.980 Try agent: Yes; Agent forwarding: No; TIS/CryptoCard: No; KI: Yes; GSSAPI: Yes
. 2020-04-01 09:08:49.980 GSSAPI: Forwarding: No; Libs: gssapi32,sspi,custom; Custom:
. 2020-04-01 09:08:49.981 Ciphers: aes,chacha20,blowfish,3des,WARN,arcfour,des; Ssh2DES: No
. 2020-04-01 09:08:49.981 KEX: ecdh,dh-gex-sha1,dh-group14-sha1,rsa,WARN,dh-group1-sha1
. 2020-04-01 09:08:49.981 SSH Bugs: Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto,Auto
. 2020-04-01 09:08:49.981 Simple channel: Yes
. 2020-04-01 09:08:49.981 Return code variable: Autodetect; Lookup user groups: Auto
. 2020-04-01 09:08:49.981 Shell: default
. 2020-04-01 09:08:49.981 EOL: LF, UTF: Auto
. 2020-04-01 09:08:49.981 Clear aliases: Yes, Unset nat.vars: Yes, Resolve symlinks: Yes; Follow directory symlinks: No
. 2020-04-01 09:08:49.981 LS: ls -la, Ign LS warn: Yes, Scp1 Comp: No; Exit code 1 is error: No
. 2020-04-01 09:08:49.981 Local directory: default, Remote directory: home, Update: Yes, Cache: Yes
. 2020-04-01 09:08:49.981 Cache directory changes: Yes, Permanent: Yes
. 2020-04-01 09:08:49.981 Recycle bin: Delete to: No, Overwritten to: No, Bin path:
. 2020-04-01 09:08:49.981 DST mode: Unix;Timezone offset: 0h 0m
. 2020-04-01 09:08:49.981 --------------------------------------------------------------------------
. 2020-04-01 09:08:50.024 Looking up host "******" for SSH connection
. 2020-04-01 09:08:50.024 Connecting to ******* port 22
. 2020-04-01 09:08:50.052 We claim version: SSH-2.0-WinSCP_release_5.17.2
. 2020-04-01 09:08:50.052 Remote version: SSH-1.99-WeOnlyDo 2.5.5
. 2020-04-01 09:08:50.052 Using SSH protocol version 2
. 2020-04-01 09:08:50.055 No GSSAPI security context available
. 2020-04-01 09:08:50.056 Have a known host key of type rsa2
. 2020-04-01 09:08:50.058 Doing ECDH key exchange with curve Curve25519 and hash SHA-256
. 2020-04-01 09:08:50.155 Server also has ssh-dss host key, but we don't know it
. 2020-04-01 09:08:50.155 Host key fingerprint is:
. 2020-04-01 09:08:50.155 ssh-rsa 1024 71:a4:b0:1d:cf:0b:c4:db:2f:6d:f8:14:5d:8b:04:e8 hbZRATyXZoHmXKZRdT+rScpfuFJCrIvHIr944K/6amU=
. 2020-04-01 09:08:50.209 Host key matches cached key
. 2020-04-01 09:08:50.210 Initialised AES-256 SDCTR (AES-NI accelerated) outbound encryption
. 2020-04-01 09:08:50.210 Initialised HMAC-SHA-256 outbound MAC algorithm
. 2020-04-01 09:08:50.210 Initialised AES-256 SDCTR (AES-NI accelerated) inbound encryption
. 2020-04-01 09:08:50.210 Initialised HMAC-SHA-256 inbound MAC algorithm
! 2020-04-01 09:08:50.211 Using username "*********".
. 2020-04-01 09:08:50.224 Server offered these authentication methods: password
. 2020-04-01 09:08:50.224 Prompt (password, "SSH password", <no instructions>, "&Password: ")
. 2020-04-01 09:09:00.180 Sent password
. 2020-04-01 09:09:00.181 Access granted
. 2020-04-01 09:09:00.182 Opening main session channel
. 2020-04-01 09:09:00.182 Opened main channel
. 2020-04-01 09:09:00.276 Attempt to close connection due to fatal exception:
* 2020-04-01 09:09:00.276 Authentication log (see session log for details):
* 2020-04-01 09:09:00.276 Using username "*******".
* 2020-04-01 09:09:00.276 (EAccessViolation) Access violation at address 0155D150 in module 'WinSCP.exe'. Read of address 00000008
. 2020-04-01 09:09:00.276 Closing connection.
* 2020-04-01 09:09:00.298 (EFatal) **Invalid access to memory.**
* 2020-04-01 09:09:00.298
* 2020-04-01 09:09:00.298 Please help us improving WinSCP by reporting the error on WinSCP support forum.
* 2020-04-01 09:09:00.298 Stack trace:
* 2020-04-01 09:09:00.298 (00BCC150) _conf_get_bool
* 2020-04-01 09:09:00.298 (00F85292) C5296_3
* 2020-04-01 09:09:00.298 (00F872FA) ____ExceptionHandler
* 2020-04-01 09:09:00.298 (00F840B4) __ExceptionHandler
* 2020-04-01 09:09:00.298 (00087D7F) ntdll.dll
* 2020-04-01 09:09:00.298 (00073221) ntdll.dll.KiUserExceptionDispatcher
* 2020-04-01 09:09:00.298 (00BD4000) _mainchan_new
* 2020-04-01 09:09:00.298 (00BEB9F1) _ssh2_serverside_agent_open
* 2020-04-01 09:09:00.298 (00BEA09A) _ssh2_connection_new
* 2020-04-01 09:09:00.298 (00BEA318) _ssh2_connection_new
* 2020-04-01 09:09:00.298 (00BFD149) _ssh_ppl_free
* 2020-04-01 09:09:00.298 (00BCBC36) C2603_0
* 2020-04-01 09:09:00.298 (00BCBD29) _run_toplevel_callbacks
* 2020-04-01 09:09:00.298 (00D05668) TSecureShell::EventSelectLoop
* 2020-04-01 09:09:00.298 (00D0454B) TSecureShell::WaitForData
* 2020-04-01 09:09:00.298 (00CFF509) TSecureShell::Init
* 2020-04-01 09:09:00.298 (00CFEE49) TSecureShell::Open
* 2020-04-01 09:09:00.298 (00D86F65) TTerminal::Open
* 2020-04-01 09:09:00.298 (00CBEA27) TTerminalThread::TerminalOpenEvent
* 2020-04-01 09:09:00.298 (00CB9984) TSignalThread::Execute
* 2020-04-01 09:09:00.298 (000BBE8F) Userinterface::C20_0
* 2020-04-01 09:09:00.298 (00015357) KERNEL32.DLL.BaseThreadInitThunk
* 2020-04-01 09:09:00.298 (00066B72) ntdll.dll.RtlGetAppContainerNamedObjectPath
* 2020-04-01 09:09:00.298 (00066B3F) ntdll.dll.RtlGetAppContainerNamedObjectPath
* 2020-04-01 09:09:00.298 Authentication log (see session log for details):
* 2020-04-01 09:09:00.298 Using username "*******".
* 2020-04-01 09:09:00.298
* 2020-04-01 09:09:00.298 Authentication failed.
What could be the issue here?