OK, so a good query to see almost all the raw data about one quiz attempt is https://docs.moodle.org/dev/Overview_of_the_Moodle_question_engine#Detailed_data_about_an_attempt.
What I am expecting that you will find is that the qu.preferredbehaviour and qa.behaviour columns are all 'deferredcbm'.
If so, it may be possible to fix it as follows. However, this is an educated guess, and I strongly recommend you test it on some data that you don't mind corrupting before doing it for real.
One way to test would be if you can take a copy of your entire Moodle site onto a test server. (This is a good thing to know how to do, becuase this is essentialy what you would have to do if you ever needed to restore your Moodle site from a backup. The steps are a combination of https://docs.moodle.org/38/en/Site_backup and https://docs.moodle.org/38/en/Moodle_migration. You probably already know this, but it does not hurt to repeat it.)
The other way you could could test the steps below is to make a new test course on your real server. Make a quiz in there, set to 'Deferred feedback with CBM behaviour'. Log in as a student and make an attempt. Then you can test with that attempt. However, testing anything on your live server is always risky.
OK, so the steps that might possibly let you change the question behaviour after an attempt has been started:
- Find the one row in the question_usages table that corresponds to the quiz attempt of interest. This will be the one where question_usages.id = quiz_attempts.uniqueid.
- In this row, change preferred_behaviour to the correct value for the behaviour you want. E.g. 'adaptive'.
- The find the corresponding rows in the question_attempts table. There should be one row for each question in the quiz. These are the rows where question_attempts.questionusageid = question_usages.id.
- In each of these rows that currently have the wrong behaviour set, change it to the right one.
- Then, log in to Moodle. Go to the quiz -> Results -> Grades report, and re-grade the attempt.
- Re-run the database query I linked to above, which shows all the raw data, to see what the affect of doing that is.
- In Moodle, review the quiz attempt and see how it looks.
As I say, this might work, even thoug it is not supported. Step 4 is tricky, becuase you have to know what the right behaviour is. For example, if you have any Essay questions in your quiz, then will always use 'manualgraded' behaviour and you should never change that. Similarly, if you have any 'Description' items, the behaviour should never be changed from 'informationitem'. Then for some combination of preferredbehaviour and question type, a different behaviour will be used in the question_attempt. For example if the preferredbehaviour is 'interactive' and the question type is something like 'match', then the question_attempt behaviour will be 'interactivecountback'.
Acutally, probably the reliable way to find what the behaviour should be for each question_attempt is to change the quiz setting to the one you want, an then start a new attempt at the quiz. Then you can see which behaviour is used for each question_attempt in that new quiz attempt.
Note, there is a feature request to implement this 'Change behaviour of an attempt that was already made' thing proplery. It is MDL-37949. However, don't hold your breath for that.