Tested under Opigno 2.5 (Drupal 8).
Affected: Fill in the blanks 1.11
Replication: Create exercise with 5-7 blanks, each with 3 alternative answers. When student is done with this exercise and clicks "next" his answers cannot be saved to the database due to "data too long for column".
From what I understand H5P tries to save to the database an array of sets of correct answers which grows 2x with each alternative answer. This behaviour is irrelevant whether you put all your blanks into one text block or into separate text blocks.