I have seen many questions like this ones and I have tried all the solutions…

Here is my setup:

1-I have a custom entity with the id defined as follow:

 * @ContentEntityType(  *   id = "bank_operation",  *   label = @Translation("Bank Operation"), 

2- My hook_theme():

function bank_operation_theme() {   return [     'bank_operation' => [       'render element' => 'elements',      ],   ]; } 

3- My hook_theme_suggestions_HOOK()

function bank_operation_theme_suggestions_bank_operation(array $  variables) {   $  suggestions = [];   $  sanitized_view_mode = strtr($  variables['elements']['#view_mode'], '.', '_');   $  suggestions[] = 'bank_operation__' . $  sanitized_view_mode;   return $  suggestions; } 

4- My Route to display the entity with a "receipt" view mode

entity.bank_operation.receipt:   path: '/bank_operation/receipt/{bank_operation}'   defaults:     _entity_view: bank_operation.receipt     _title: 'Receipt'   requirements:     _entity_access: 'bank_operation.view' 

5-My twig files:

modules/custom/bank_operation/templates/bank-operation.html.twig modules/custom/bank_operation/templates/bank-operation--receipt.html.twig 

Result: Everything works fine :

–receipt view mode is used

-suggestions seems to be correctly added:

<!-- THEME HOOK: 'bank_operation' --> <!-- FILE NAME SUGGESTIONS:    x bank-operation.html.twig    * bank-operation--receipt.html.twig    x bank-operation.html.twig --> <!-- BEGIN OUTPUT from 'modules/custom/bank_operation/templates/bank-operation.html.twig' --> 

Except that bank-operation--receipt.html.twig is not called

I have tried all combinations of file name/suggestions/base hook name/… without any success

I have added all the possible twig file name in my templates folder (with or without dash)

I have the feeling that the problem is coming from the fact that the ID of my entity have an underscore in its name…