I tried the hotfix and got a disconnected by the server.
Here's the log:
2020-04-15 08:49:34.425 Opening log file.
2020-04-15 08:49:34.471 INFO FileLogWriter(1)[1] Info: Assembly: Rebex.Common (Hotfix Build 7410) for .NET 3.5 SP1
2020-04-15 08:49:34.487 INFO FileLogWriter(1)[1] Info: Platform: Windows 6.2.9200 64-bit; CLR: 2.0.50727.8689
2020-04-15 08:49:34.487 DEBUG FileLogWriter(1)[1] Info: Culture: de; Windows-1252
2020-04-15 08:49:36.248 INFO Sftp(1)[1] Info: Connecting to --.--.--:22 using Sftp.
2020-04-15 08:49:36.248 INFO Sftp(1)[1] Info: Assembly: Rebex.Sftp (Hotfix Build 7410) for .NET 3.5 SP1 (Trial)
2020-04-15 08:49:36.248 INFO Sftp(1)[1] Info: Platform: Windows 6.2.9200 64-bit; CLR: 2.0.50727.8689
2020-04-15 08:49:36.248 DEBUG Sftp(1)[1] Info: Culture: de; Windows-1252
2020-04-15 08:49:36.264 DEBUG Sftp(1)[1] Proxy: Resolving '--.--.--'.
2020-04-15 08:49:36.310 DEBUG Sftp(1)[1] Proxy: Connecting to 111.111.111.111:22 (no proxy).
2020-04-15 08:49:36.342 DEBUG Sftp(1)[1] Proxy: Connection established.
2020-04-15 08:49:36.389 DEBUG Sftp(1)[1] SSH: Server is 'SSH-2.0-8.37 FlowSsh: Bitvise SSH Server (WinSSHD) 8.37'.
2020-04-15 08:49:36.404 INFO Sftp(1)[1] SSH: Negotiation started.
2020-04-15 08:49:36.654 DEBUG Sftp(1)[1] SSH: Negotiating key.
2020-04-15 08:49:36.701 INFO Sftp(1)[4] SSH: Disconnected by the server ('').
2020-04-15 08:49:36.717 ERROR Sftp(1)[1] SSH: Negotiation failed. Disconnected by the server ('').
2020-04-15 08:49:36.905 ERROR Sftp(1)[1] Info: Rebex.Net.SshException: Disconnected by the server ('').
bei Rebex.Net.SshSession.blhp[dg,dh](gxyv`2 ans, Int32 ant, gxyw anu, dh anv, dg anw, dg anx)
bei Rebex.Net.SshSession.blho[dg,dh](gxyv`2 anq, dh anr)
bei Rebex.Net.SshSession.blhw(gmmg aog)
bei gmmm.kqfk(SshSession fck, Byte[] fcl, Byte[] fcm, Byte[] fcn, Byte[] fco, gmlz& fcp, Byte[]& fcq, SshPublicKey& fcr)
bei Rebex.Net.SshSession.blhy(Byte[] aoh)
bei Rebex.Net.SshSession.Negotiate()
bei Rebex.Net.Sftp.mcix.tmlm(xboz wl, Boolean wm)
bei Rebex.Net.Sftp.hnpo(String lu, Int32 lv, SshParameters lw, xboz lx)