Despite its name referencing a Layer-2 destination-address or header level mismatch, the MIB's own description ties this drop specifically to the receiving port not being in STP forwarding state at the moment the frame arrived. This distinguishes CFM frames lost to normal topology convergence, as a port transitions through blocking or listening, from frames lost to an actual MD-level addressing error, which would otherwise both look like generic dropped CFM frames. A short burst here that coincides with an STP topology-change log entry is benign; the same burst with no nearby STP event instead warrants checking the L2 header or MD-level configuration.