csvlink appears to hang during training

csvlink hangs after a few seconds with 0.0% CPU

• python version: 3.7.3
• environment: centos

CSV Files to Match

$ wc -l train-*
   494 train-left.csv
   481 train-right.csv

Config file

Attempting to match on 9 fields.

{
 "field_names": [
  "state",
  "email",
  "address_2",
  "address_1",
  "county",
  "postal_code",
  "city",
  "name"
 ],
 "field_definition": [
  {
   "field": "state",
   "type": "String",
   "Has Missing": true
  },
  {
   "field": "email",
   "type": "String",
   "Has Missing": true
  },
  {
   "field": "address_2",
   "type": "String",
   "Has Missing": true
  },
  {
   "field": "address_1",
   "type": "String",
   "Has Missing": true
  },
  {
   "field": "county",
   "type": "String",
   "Has Missing": true
  },
  {
   "field": "postal_code",
   "type": "String",
   "Has Missing": true
  },
  {
   "field": "city",
   "type": "String",
   "Has Missing": true
  },
  {
   "field": "name",
   "type": "String",
   "Has Missing": true
  }
 ],
 "output_file": "deduped.csv",
 "skip_training": false,
 "training_file": false,
 "sample_size": 150000,
 "recall_weight": 2
}

Command

Running csvlink with the following:

csvlink train-left.csv train-right.csv --config_file=config.json --inner_join

After an initial large cpu hit, the script settles down into a very relaxed state:

PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
14191 somebody+  20   0  558660 143092  10144 S   0.0  0.9   0:52.45 csvlink

Am I doing something wrong?