Yes, setting the Features per Transactions did resolve the problem.Also creating the table before inserting the data, instead of having FME create the table helped.

There is a "Features Per Transaction" parameter on the PostGIS Writer - try setting this to 1.If this is >1, the workspace might be triggering a bulk insert.If this is the case, the first job will issue table-level lock in PostGIS, which will cause the subsequent jobs to fail.If "Features Per Transaction" = 1, each job should only issue a row-level lock in PostGIS for each feature, as it is being written.This will not prevent the other jobs from writing to the same table.