A previous posting by you that showed logs indicated a client using a smart phone ... was that you attempting admin stuff?
Performance_schema should be activated.
ℹ Sys schema is not installed.
performance_schema=ON
InnoDB buffer pool / data size: 8.0G / 5.9G
innodb_buffer_pool_instances: 1
Should be 8 ... 1 per buffer pool?
https://releem.com/docs/mysql-performance-tuning/innodb_buffer_pool_instances
innodb_buffer_pool_instances
Considerations
The reason to break the InnoDB buffer pool into instances is straightforward. By dividing the buffer pool, concurrency is improved so there is less contention between threads. Every instance takes an equal section of the buffer pool, so if innodb_buffer_pool_size is set to 8GB and innodb_buffer_pool_instances is set to 4, then each instance is 2GB. Ideally, each instance should be a minimum of 1GB in size.
In code/admin/cli/ run the following ...
adhoc_task.php
fix_orphaned_question_categories.php
check_database_schema.php
checks.php with -v
Am guessing, but appears you are getting ready for fall semester and your process with courses is to restore a no-user course backup for the new courses?
The course restores that failed ... are those the same courses that have quiz issues?
Instead, make one backup of a course and archive - that's the records retention archive. You could do that from command line (backup.php in code/admin/cli) for all courses saving to a directory outside of moodledata/filedir/
Then, use course reset - removing all students their work leaving only teachers and content.
That will avoid quiz bank duplication.
'SoS', Ken