The test failed once on Buildbot with the result difference:

 # ib_logfile0 expecting FOUND
-FOUND 3 /public|gossip/ in ib_logfile0
+FOUND 2 /public|gossip/ in ib_logfile0

The most plausible explanation for this difference
should be that the redo log payload grew was so big that
one of the strings (for writing the undo log record,
clustered index record, and secondary index record)
was written to ib_logfile1 instead of ib_logfile0.

Let us run the test with --innodb-log-files-in-group=1 so that
only a single log file will be used.

mysql-test/suite/encryption/r/innodb_encrypt_log.result

@@ -37,8 +37,6 @@ NOT FOUND /private|secret|sacr(ed|ament)|success|story|secur(e|ity)/ in ibdata1
 NOT FOUND /private|secret|sacr(ed|ament)|success|story|secur(e|ity)/ in t0.ibd
 # ib_logfile0 expecting NOT FOUND
 NOT FOUND /private|secret|sacr(ed|ament)|success|story|secur(e|ity)/ in ib_logfile0
-# ib_logfile1 expecting NOT FOUND
-NOT FOUND /private|secret|sacr(ed|ament)|success|story|secur(e|ity)/ in ib_logfile1
 # Restart without redo log encryption
 SELECT COUNT(*) FROM t0;
 COUNT(*)

mysql-test/suite/encryption/t/innodb_encrypt_log.opt

@@ -3,4 +3,5 @@
 --plugin-load-add=$FILE_KEY_MANAGEMENT_SO
 --loose-file-key-management
 --loose-file-key-management-filename=$MYSQL_TEST_DIR/std_data/logkey.txt
+--innodb-log-files-in-group=1
 --file-key-management-encryption-algorithm=aes_cbc

mysql-test/suite/encryption/t/innodb_encrypt_log.test

@@ -57,9 +57,6 @@ INSERT INTO t0
 --echo # ib_logfile0 expecting NOT FOUND
 -- let SEARCH_FILE=$MYSQLD_DATADIR/ib_logfile0
 -- source include/search_pattern_in_file.inc
---echo # ib_logfile1 expecting NOT FOUND
--- let SEARCH_FILE=$MYSQLD_DATADIR/ib_logfile1
--- source include/search_pattern_in_file.inc
 
 --echo # Restart without redo log encryption
 -- let $restart_parameters=--skip-innodb-encrypt-log --innodb-log-files-in-group=1