When setting tables in an app form, keep in mind that tables have the following limitations.

• Fields inside a table cannot be set for Key Field or Field Mappings in the "Lookup" field settings.
  Configuring a "Lookup" Field
  Fields That Can Be Specified for "Field Mappings"
• Fields inside a table cannot be set for Fetch Criteria in the "Related records" field settings.
  Field that Can Be Specified for the "Fetch Criteria" Setting in Related Records
• When you include references to a field inside a table in the formula of a field that is not in a table, functions that can be used in the formula are only SUM and CONTAINS.
  SUM Function: Calculate the Total of Numeric Values
  CONTAINS Function: Determine If a Field Contains an Exact Match for a Specified Character String
  List of Operators and Functions
• If you set Record permalink as a source field in the Field Mappings section in the app's Action setting, fields inside a table cannot be set as the corresponding destination field.
  Available Field Combinations for App Actions
• Fields inside a table cannot be set as the Title Field.
  Setting Title Field
• It is not possible to set permissions for fields inside a table in the Permissions for Fields setting.
  Configuring Permissions for Fields

• If a table contains an "Attachment" field, data in the table cannot be bulk updated.
  Checking the Destination App for File Import

• Data in a table cannot be bulk updated if the table contains a "Lookup" field whose field settings are configured as follows: a field for which Prohibit duplicate values is disabled is set for Key Field, or a field for which you do not have view permission is set for Datasource App.
  Checking the Destination App for File Import

• Tables cannot be placed in a "Field group" field.
  The "Field group" field
• Once you click Activate App or Update App after placing fields, these fields cannot be placed in a table.
• It is not possible to sort data of fields inside a table.
  Which fields and items can be used for "Sort by"?