Cassandra: I see ALTER TABLE ... in the logs but why ? Is it Cassandra internal

Question

I am monitoring a system, and in Cassandra I see lots of

ALTER TABLE tbl-name ADD column-name type

The legacy code I am going through I cannot see any ALTER TABLE So either Cassandra is synchronising somehow between nodes OR I have people in my env doing funky stuff

Any ideas how to figure out from where these ALTER commands are coming from ?

Using Cassandra 3.11, Scala, and Phantom DSL 1.28