Cygwin sshd broken by seemingly trivial network change

[worsafe@bellsouth.net]

While installing a new router, I changed my local network from 
192.168.4.* to 192.168.50.*. This seems to have broken Cygwin sshd on 
both of my remote computers, but only for Cygwin; sshd works fine if I 
boot the remote computer from a linux thumb drive. I have noticed no 
other problems with the new network configuration.
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ssh -vvv does not give any messages that look useful to me. 
Authentication problems usually give some useful message, but this seems 
to fail before getting that far:

ssh -vvv $ASUS12
OpenSSH_8.3p1, OpenSSL 1.1.1f 31 Mar 2020
debug1: Reading configuration data /home/cdr/.ssh/config
debug1: /home/cdr/.ssh/config line 1: Applying options for *
debug1: Reading configuration data /etc/ssh_config
debug2: resolve_canonicalize: hostname 192.168.50.105 is address
debug2: ssh_connect_direct
debug1: Connecting to 192.168.50.105 [192.168.50.105] port 22.
debug1: connect to address 192.168.50.105 port 22: Connection timed out
ssh: connect to host 192.168.50.105 port 22: Connection timed out
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The server is running, as confirmed by cyrunsrv -Q sshd.
/var/log/sshd.log is an empty file.
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nmap shows port 22 open on the remote server:
nmap -p22 $ASUS12
Nmap scan report for asus12 (192.168.50.105)
Host is up (0.13s latency).
PORT STATE SERVICE
22/tcp filtered ssh
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However, telnet fails before returning the expected header string:
telnet $ASUS12 22
Connecting To 192.168.50.105...Could not open connection to the host, on 
port 22
: Connect failed
(For comparison, linux returns the string "SSH-2.0-OpenSSH_7.9p1 
Debian-10+deb10u2")
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I can't think what to try short of reinstalling sshd.