Decapsulate error InvalidCounter (not a huge problem, just curious why it happens and whether I should worry)

I run boringtun-cli based configuration. It works and works very good so far.

However, the stdout from boringtun-cli running in foreground (default verbosity, just keeping eye on it) shows

Decapsulate error InvalidCounter

About 10-20 new errors per hour.

It does not appear to degrade connection or anything.

What is this error and should I be concerned?