DynamoDB stream triggered lambda not works

Question

There are two DynamoDB tables and two Lambdas. One table is configured with DynamoDB Stream to trigger one of the Lambda, and similarly the other table triggers the other Lambda. However, when changes are made to the tables, only the first Lambda works successfully. The other one is not triggered (no CloudWatch log).

There's no difference with the stream configurations. There's no difference with the insert/update item logic. The only difference is the table schema. The item inserts/updates were all successful.

What could possibly be wrong?

Also if I insert/update the item with AWS console manually, it triggered the second Lambda successfully. The first successful lambda works immediately, while the second lambda works few minutes later.

Code used to insert/update item with boto3:

# insert/update dynamodb item with python boto3

PRODUCT_TABLE.update_item(
  Key = {'PRODUCT_NO': 1, 'TYPE': 'a'},
  UpdateExpression = "set DATETIME=:DATETIME",
  ExpressionAttributeValues = {':DATETIME': '0000-~~'}
)

OPTION_TABLE.update_item(
  Key = {'OPTION_NO': 1, 'TYPE': 'a'},
  UpdateExpression = "set FLAG1=:FLAG1, FLAG2=:FLAG2",
  ExpressionAttributeValues = {':FLAG1': None, ':FLAG2': True}
)

# Table that successfully triggers the Lambda

PRODUCT table
PRODUCT_NO (Number)
TYPE (String)
DATETIME (String)
... several columns

PRODUCT_LOG table
LOG_DATETIME (String)
LOG_TYPE (String)
... same columns with PRODUCT table

# Table that does not successfully triggers the Lambda

OPTION table (there's only 4 columns)
OPTION_NO (Number)
TYPE (String)
FLAG1 (null or not set)
FLAG2 (bool)

OPTION_LOG table
LOG_DATETIME (String)
LOG_TYPE (String)
... same columns with OPTION table