dmlwriteexception with course restoration

Hello

Were are restoring a  course on a new Moodle project, from 3.3 to 3.5.1
When restoring, I have a dmlwriteexception for a duplicate entry.

Here is the error code : 

Duplicate entry '321hm' for key 'mdl_quesnumeunit_queuni_uix'
INSERT INTO mdl_question_numerical_units (multiplier,unit,question) VALUES(?,?,?)
[array (
0 => '1.00000000000000000000',
1 => 'ohm',
2 => 3218,
)] 
Error code: dmlwriteexception

I've deleted the question in questions.xml, but it makes me the same error for an other question.

If I repeat the restore process, it's never the same key. 

The next time it will be 3219-ohm, after 3220...

-----

max_allowed_packet = 8000M

character-set-server = utf8mb4

innodb_file_format = Barracuda

How can I solve the problem ?

Thanks