Form elements that have parent are renamed, by adding '_' and pid during webform migration (D7Webform.php lines 243-245.
So during submission migration, wrong form_key are used, and no values are displayed.
In drupal 7 create a webform with elements regrouped under groups (like in 2021-09-27 16_19_25-Formulaire Maillots.png screenshot)
Migrate to Drupal 8. Most fieldnames are renamed (see 2021-09-27 16_24_24-Maillots 2020 _ verif2.png).
For example taille_8ans become taille_8ans_13, but remis stay remis.
During submission import values submitted are affected to orignal fieldname.
During submission import search webform elements named with the original fieldname + '_' and pid
Needs review
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