SFTP and Key compatibility

[tocguy]

Two Linksys EA3500s both running OpenWrt stable build 21.02. One main router and one dumb AP.
With the addition of openssh-sftp-server on each I've been able to transfer files using SFTP. All good...until today.
The dumb AP will also allow connection via Putty SSH using "root" and password. No problem.
The dumb AP will allow connection via SFTP using same "root" and password. No problem.
The main router will allow connection via Putty SSH using its "root" and password. No problem.
The main router will NOT allow connection via SFTP using its same "root" and password. That's a problem.

Re-installed openssh-sftp-server and rebooted but it did not change the outcome.
Prior to this issue I added a OpenSSH key to both devices and it successfully permits autologon from Putty for both devices.

Is this a reset & start over or is their some other valuable troubleshooting I can learn from?

TIA

[vgaetera]

ubus call system board; \
opkg list-installed | grep -e dropbear -e openssh; \
ls -l $(opkg files openssh-sftp-server | sed -e 1d); \
ls -a -l /etc/dropbear; uci show dropbear; \
netstat -l -n -p | grep -e dropbear; \
pgrep -f -a dropbear

[tocguy]

Augh! This helped me to solve the problem. While the reason for the early connection issues is still a mystery your commands did reveal that I'd F'd up when re-installing the SFTP package. Apparently, I mistakenly installed the client rather than the server. FIX: Purge client, install server and I'm back in business.

dropbear - 2020.81-2
openssh-sftp-client - 8.4p1-4
Collected errors:
 * opkg_files_cmd: **Package openssh-sftp-server not installed.**

Big thank you for this learning experience.