Using a non CDB / PDB Oracle DB, debezium fetches initially all the rows. All subsequent updates gets lost. Was debezium tested with non-CDB (SID-based) databases? Initially I got the:

Caused by: java.lang.IllegalArgumentException: No metadata registered for captured table "XYZ.AIRHACKS.ATABLE" exception. After changing the connector.properties, the exception disappears, but all subsequent changes are ignored.

However: "XYZ" is the name of the oracle server what could be the actual problem. With Oracle CDB debezium works perfectly.

See attached log file

Used database:

Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
PL/SQL Release 12.2.0.1.0 - Production
"CORE        12.2.0.1.0        Production"
TNS for IBM/AIX RISC System/6000: Version 12.2.0.1.0 - Production
NLSRTL Version 12.2.0.1.0 - Production