There are a couple of things I would check as per the error:
1. Check whether the Server (where the Solarwinds is running) and the switches are pingable. It might be possible that there is connectivity between the device and the switch from where you are doing SSH, however there are issues between the Solarwinds Server and the switch.
2. I would change the Config Min length to the maximum possible value and see if I am still getting the error.
You may try these steps, and let us know if it works or not. Even if you resolve the issue through some different troubleshooting.
Would appreciate if you could post the resolution here, so that it helps others.
Good Luck resolving the issue !!!