Training validation stops after a couple of steps


I was trying to set up my pipeline to output tensorboard logs, however I noticed in the graphs that the validation metrics stop after a couple of steps, whereas the training metrics continue

I can also see it happening in the terminal, where at some point all the val_ metrics disappear.

Here is my config:

language: en

   - name: WhitespaceTokenizer
   - name: RegexFeaturizer
   - name: LexicalSyntacticFeaturizer
   - name: CountVectorsFeaturizer
   - name: CountVectorsFeaturizer
     analyzer: char_wb
     min_ngram: 1
     max_ngram: 4
   - name: DIETClassifier
     batch_size: 32
     epochs: 20
     constrain_similarities: true
     evaluate_on_number_of_examples: 880 # 15% of the data for validation
     evaluate_every_number_of_epochs: 2
     tensorboard_log_directory: "models/tensorboard/v4"
     tensorboard_log_level: "epoch"
   - name: EntitySynonymMapper
   - name: FallbackClassifier
     threshold: 0.3
   - name: ResponseSelector
     epochs: 5
     evaluate_every_number_of_epochs: 1
     evaluate_on_number_of_examples: 20
     constrain_similarities: true

   - name: MemoizationPolicy
   - name: RulePolicy
     core_fallback_threshold: 0.6
     core_fallback_action_name: action_default_fallback
     enable_fallback_prediction: true
   - name: TEDPolicy
     max_history: 7
     epochs: 1
     constrain_similarities: true