The error is: 

dead_error_condition: The switch governing value op_type cannot be _OPERATION_TYPE_COUNT.

CID 114074 (#1 of 1): Logically dead code (DEADCODE)dead_error_begin: Execution cannot reach this statement: case _OPERATION_TYPE_COUNT:.

WT-5733 tried to address an issue raised by Coverity: 

https://coverity.corp.mongodb.com/reports.htm#v16729/p10049/fileInstanceId=35867688&defectInstanceId=20081907&mergedDefectId=114074&eventId=20081907-4

Despite of the changes, Coverity still complains. Using the if/else if/etc approach should fix the issue for good.

Interestingly, Coverity does not complain anymore about the switch here but only this one.