I am using a WR21 (FW: 188.8.131.52 (Mar 7 2019 07:02:27)) and am seeing the same error.
13:48:05, 09 Jan 2020,Certificate Code Error
Lib: SSL routines
Reason: sslv3 alert certificate unknown
The reason it was brought up is that our ISP (Bell Canada) has come to us indicating a very large amount of traffic from this site attempting to reach 192.168.127.2. Clearly it is not reachable, but it is still accumulating a very large amount of cellular data. Could there be a correlation between this error, and the rogue data? Of note, the times of the error appear to be similar to the times that the additional data is being generated.
Hi and welcome to Digi Forums!
The certificate error itself will not generate traffic, however, this error is potentially due to incoming traffic trying to reach the router using ssh or https and those will generate traffic.
If the device has a public IP address, the above is likely what is causing this and improving security on the device, such as configuring and enabling the firewall would help, see our TransPort security lock down document here: ftp://ftp1.digi.com/support/documentation/AN_018_TransPort_Security_Lockdown.pdf
Without seeing complete logs from the device, it will be hard to comment further.
For any further help or investigation on that issue, please review our support options on our website: https://www.digi.com/support and mail our support team at firstname.lastname@example.org.
Digi Technical Support Engineer