What Debezium connector do you use and what version?

"class": "io.debezium.connector.db2as400.As400RpcConnector",
"type": "source",
"version": "3.0.8.Final"

Explanation

The current implementation of the IBMI Debezium source connector only allows value trimming on all leading AND trailing padding. In some circumstances, database values may contain leading whitespace, which would then be truncated. This default behavior can be detrimental to data integrity. Therefore it should be considered to add a new configuration method to trim trailing padding only. This optional configuration parameter will ensure that all leading padding characters are preserved from the DB2 database to the Debezium Kafka output.

More Information:
#community-ibmi > Debezium Source connector IBM I Series Leading Whitespace