by Ken Task.
Check what's in moodledata/temp/backup/ and also in trashdir
Then ... what happens if ...
cd code//admin/tool/task/cli/
Create a bash shell script called 'cleanup' which contains
php schedule_task.php --execute="\core\task\backup_cleanup_task";
php schedule_task.php --execute="\core\task\file_temp_cleanup_task";
php schedule_task.php --execute="\tool_recyclebin\task\cleanup_category_bin";
php schedule_task.php --execute="\tool_recyclebin\task\cleanup_course_bin";
then check moodledata/temp/backup/ and moodledata/trashdir/
Above won't fix ... more exploring what's there and might lead to other discoveries!
'SoS', Ken