9.5 to 9.6: ORA-01430: column being added already exists in table

Hi. Our app fails to start on one of the on-premises environments after we upgraded from 9.5 to 9.6. The other two environments work well. The only difference is that we deploy less often to the failing environment. It prints: 12:33:14.090: [APP/PROC/WEB.0] INFO - Core: Executing DDL commands... 12:33:14.091: [APP/PROC/WEB.0] INFO - ConnectionBus: Executing 182 database synchronization command(s)... 12:33:14.135: [APP/PROC/WEB.0] ERROR - M2EE: An error occurred while executing action 'Execute DDL commands'. 12:33:14.135: [APP/PROC/WEB.0] ERROR - M2EE: com.mendix.m2ee.api.AdminException: Executing DDL commands failed. 12:33:14.135: [APP/PROC/WEB.0] at com.mendix.basis.component.internal.LocalComponentImpl.executeDDLCommands(LocalComponentImpl.scala:120) 12:33:14.135: [APP/PROC/WEB.0] Caused by: com.mendix.basis.connectionbus.ConnectionBusException: Error (SQL State: 72000, Error Code: 1430) on executing: 12:33:14.135: [APP/PROC/WEB.0] ALTER TABLE "SYSTEM$QUEUEDTASK" ADD "CONTEXTDATA" nclob NULL 12:33:14.135: [APP/PROC/WEB.0] All changes are rolled back. 12:33:14.135: [APP/PROC/WEB.0] at com.mendix.connectionbus.modelsynchronization.DdlCommandExecutor.handleCommandExecutionException(DdlCommandExecutor.scala:149) 12:33:14.135: [APP/PROC/WEB.0] Caused by: java.sql.SQLException: ORA-01430: column being added already exists in table 12:33:14.136: [APP/PROC/WEB.0] at oracle.jdbc.driver.T4CTTIoer11.processError(T4CTTIoer11.java:630) How to troubleshoot this?   I tried to manually drop this and the other columns it was failing to add, also I had to drop the tables with bogus names like "7A49E0540D4142A2B9B8390C0DE343" because they had conflicting indexes and finally the error is: Could not find child entity with id 5c570d3b-7b31-44fe-abd6-269a234584c5 for association System.Workflow_WorkflowDefinition  
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