Assertion `block->page.flush_observer == __null || block->page.flush_observer == observer' failed in buf_flush_note_modification

--mysqld=--innodb-encrypt-tables  --mysqld=--innodb-encryption-threads=4    --mysqld=--file-key-management  --mysqld=--plugin-load-add=file_key_management --mysqld=--file-key-management-filename=`pwd`/std_data/keys.txt --mysqld=--plugin-load-add=file_key_management --repeat=5 --mem

--source include/have_innodb.inc

SET @scrub.save= @@innodb_background_scrub_data_uncompressed;

--connect (con1,localhost,root,,)

CREATE TABLE t1 (pk INT, a INT, PRIMARY KEY(pk)) ENGINE=InnoDB;

INSERT INTO t1 VALUES (1,2),(2,3),(3,4),(4,5),(5,6),(6,7),(7,8),(8,9);

SET GLOBAL innodb_background_scrub_data_uncompressed=ON;

--disconnect con1

--connection default

--let $i= 1000

while ($i)

{

   --eval ALTER TABLE t1 FORCE /* $i */

   --dec $i

}

# Cleanup

--delimiter ;

DROP TABLE t1;

# This is intentionally commented, so that when you run with --repeat,

# the server is restarted every time between the runs

# SET GLOBAL innodb_background_scrub_data_uncompressed = @scrub.save;

mysqld: /data/src/10.4/storage/innobase/include/buf0flu.ic:65: void buf_flush_note_modification(buf_block_t*, lsn_t, lsn_t, FlushObserver*): Assertion `block->page.flush_observer == __null || block->page.flush_observer == observer' failed.

190906 18:34:16 [ERROR] mysqld got signal 6 ;

#7  0x00007fb27288ef12 in __GI___assert_fail (assertion=0x555abe139f18 "block->page.flush_observer == __null || block->page.flush_observer == observer", file=0x555abe139e18 "/data/src/10.4/storage/innobase/include/buf0flu.ic", line=65, function=0x555abe13bd80 <_ZZL27buf_flush_note_modificationP11buf_block_tmmP13FlushObserverE19__PRETTY_FUNCTION__> "void buf_flush_note_modification(buf_block_t*, lsn_t, lsn_t, FlushObserver*)") at assert.c:101

#8  0x0000555abd8836da in buf_flush_note_modification (block=0x7fb26782a8f8, start_lsn=484825, end_lsn=484831, observer=0x0) at /data/src/10.4/storage/innobase/include/buf0flu.ic:65

#9  0x0000555abd887420 in ReleaseBlocks::add_dirty_page_to_flush_list (this=0x7fb24d7f9780, slot=0x7fb24d7f98e8) at /data/src/10.4/storage/innobase/mtr/mtr0mtr.cc:379

#10 0x0000555abd88746f in ReleaseBlocks::operator() (this=0x7fb24d7f9780, slot=0x7fb24d7f98e8) at /data/src/10.4/storage/innobase/mtr/mtr0mtr.cc:390

#11 0x0000555abd88829e in CIterate<ReleaseBlocks const>::operator() (this=0x7fb24d7f9780, block=0x7fb24d7f98d8) at /data/src/10.4/storage/innobase/mtr/mtr0mtr.cc:60

#12 0x0000555abd887c0c in mtr_buf_t::for_each_block_in_reverse<CIterate<ReleaseBlocks const> > (this=0x7fb24d7f98a0, functor=...) at /data/src/10.4/storage/innobase/include/dyn0buf.h:371

#13 0x0000555abd886282 in mtr_t::Command::release_blocks (this=0x7fb24d7f97f0) at /data/src/10.4/storage/innobase/mtr/mtr0mtr.cc:885

#14 0x0000555abd8863c5 in mtr_t::Command::execute (this=0x7fb24d7f97f0) at /data/src/10.4/storage/innobase/mtr/mtr0mtr.cc:910

#15 0x0000555abd8845b5 in mtr_t::commit (this=0x7fb24d7f98a0) at /data/src/10.4/storage/innobase/mtr/mtr0mtr.cc:558

#16 0x0000555abdb6efdb in fil_crypt_rotate_page (key_state=0x7fb24d7f9e34, state=0x7fb24d7f9e40) at /data/src/10.4/storage/innobase/fil/fil0crypt.cc:2052

#17 0x0000555abdb6f6f4 in fil_crypt_rotate_pages (key_state=0x7fb24d7f9e34, state=0x7fb24d7f9e40) at /data/src/10.4/storage/innobase/fil/fil0crypt.cc:2179

#18 0x0000555abdb701e1 in fil_crypt_thread () at /data/src/10.4/storage/innobase/fil/fil0crypt.cc:2403

#19 0x00007fb2744034a4 in start_thread (arg=0x7fb24d7fa700) at pthread_create.c:456

#20 0x00007fb27294bd0f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:97