I've tried searching for similar issues associated with the answers field in the question_shortanswer table and they seem to imply that the field is no longer requred.
what I did was ...
Backup course and accept all the defaults. Include all the items and user data.
Course backs up ok.
On restoring course to a new course in an existing category the following error is displayed:

Debug info: Data too long for column 'answers' at row 1
INSERT INTO mdl_question_shortanswer (answers,usecase,question) VALUES(?,?,?)
[array (
0 => '2133251,2133252,2133253,2133254,2133255,2133256,2133257,2133258,2133259,2133260,2133261,2133262,2133263,2133264,2133265,2133266,2133267,2133268,2133269,2133270,2133271,2133272,2133273,2133274,2133275,2133276,2133277,2133278,2133279,2133280,2133281,2133282,2133283,2133284,2133285,2133286,',
1 => '0',
2 => 594077,
)]
Stack trace:

line 397 of /lib/dml/moodle_database.php: dml_write_exception thrown
line 973 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
line 1015 of /lib/dml/mysqli_native_moodle_database.php: call to mysqli_native_moodle_database->insert_record_raw()
line 82 of /question/type/shortanswer/backup/moodle2/restore_qtype_shortanswer_plugin.class.php: call to mysqli_native_moodle_database->insert_record()
line 131 of /backup/util/plan/restore_structure_step.class.php: call to restore_qtype_shortanswer_plugin->process_shortanswer()
line 103 of /backup/util/helper/restore_structure_parser_processor.class.php: call to restore_structure_step->process()
line 125 of /backup/util/xml/parser/processors/grouped_parser_processor.class.php: call to restore_structure_parser_processor->dispatch_chunk()
line 91 of /backup/util/helper/restore_structure_parser_processor.class.php: call to grouped_parser_processor->postprocess_chunk()
line 148 of /backup/util/xml/parser/processors/simplified_parser_processor.class.php: call to restore_structure_parser_processor->postprocess_chunk()
line 92 of /backup/util/xml/parser/processors/progressive_parser_processor.class.php: call to simplified_parser_processor->process_chunk()
line 169 of /backup/util/xml/parser/progressive_parser.class.php: call to progressive_parser_processor->receive_chunk()
line 253 of /backup/util/xml/parser/progressive_parser.class.php: call to progressive_parser->publish()
line ? of unknownfile: call to progressive_parser->end_tag()
line 158 of /backup/util/xml/parser/progressive_parser.class.php: call to xml_parse()
line 137 of /backup/util/xml/parser/progressive_parser.class.php: call to progressive_parser->parse()
line 105 of /backup/util/plan/restore_structure_step.class.php: call to progressive_parser->process()
line 153 of /backup/util/plan/base_task.class.php: call to restore_structure_step->execute()
line 148 of /backup/util/plan/base_plan.class.php: call to base_task->execute()
line 157 of /backup/util/plan/restore_plan.class.php: call to base_plan->execute()
line 315 of /backup/controller/restore_controller.class.php: call to restore_plan->execute()
line 147 of /backup/util/ui/restore_ui.class.php: call to restore_controller->execute_plan()
line 46 of /backup/restore.php: call to restore_ui->execute()

Course restores fine without quizes. The course was originally upgraded from 1.9.17

Please let me know if you require anymore information.