GG stops after upgrade to PHP 7.1.9

Are there any issues with PHP 7.1.9? (Couldn’t find any reference to this in a forum search.)

PHP has just been upgraded and Gwolle Guestbook stopped displaying on the front end at:
https://www.englishclub.com/comments/guestbook/

But it seems to work fine in the back end. The debug creates two test entries and the following readout:

WordPress version: 4.9.4 (db: 38590)
WordPress theme: ECrespo-comments
Active plugins: Array ( [0] => akismet/akismet.php [1] => gwolle-gb/gwolle-gb.php )
PHP Version: 7.1.9
MySQL Version: 5.6.33-79.0
MySQL Charset: MySQL Charset: utf8mb4
MySQL Column Charset: utf8mb4
MySQL / MySQLi: mysqli
MySQL variables: Array ( [character_set_client] => utf8mb4 [character_set_connection] => utf8mb4 [character_set_database] => utf8 [character_set_filesystem] => binary [character_set_results] => utf8mb4 [character_set_server] => utf8 [character_set_system] => utf8 [character_sets_dir] => /usr/share/mysql/charsets/ )

Deactivating Akismet didn’t help.
There are no error messages in the server error log.

Thanks

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