In the functions rtr_page_copy_rec_list_end_no_locks() and rtr_page_copy_rec_list_start_no_locks(), no redo log is being written for clearing a bit in the R-tree page:

				if (rec_get_deleted_flag(cur1_rec,

					dict_table_is_comp(index->table))) {

					goto next;

				} else {

					/* We have two identical leaf records,

					skip copying the undeleted one, and

					unmark deleted on the current page */

					btr_rec_set_deleted_flag(

						cur_rec, NULL, FALSE);

					goto next;

				}

This call is also passing page_zip=NULL, which ought to cause UNIV_ZIP_DEBUG assertion failures when using ROW_FORMAT=COMPRESSED. But, that parameter was changed in MySQL 5.7.5 exactly to address the failure of a UNIV_ZIP_DEBUG check. There code change is associated with a test case change, so we have some hope that the failure is repeatable.

The purpose of this call is unclear. It was added as part of introducing InnoDB R-tree index support.

The bug was found as part of implementing a purely physical redo log record format in MDEV-12353.