I run a multilingual site with ACF that that manages its translations through WPML. Both are made compatible through the glue plugin “Advanced Custom Fields Multilingual” by WPML’s developers.
After updating ACF to 5.7.6 and upgrading the database, I noticed that some elements on the secondary language version of the site (English, primary language is German) are missing. Those missing items are entered via custom fields for both language versions.
The german version of the fields work as expected: You fill out the fields, save and that’s it. The english fields, however, do not save any data at all. After the plugin upgrade, all english field values were wiped and any newly entered data won’t save (after hitting “save”, the fields are wiped again).
I have also noticed that enabling WordPress debugging, the logs get flooded with two new error messages:
[27-Sep-2018 06:03:49 UTC] PHP Notice: is_home wurde <strong>fehlerhaft aufgerufen</strong>. Bedingte Abfragen (Conditional Tags) funktionieren nicht, wenn die Beitrags-Abfrage (query_posts) noch nicht durchgeführt wurde. Sie geben dann immer 'false' zurück. Weitere Informationen: <a href="https://codex.wordpress.org/Debugging_in_WordPress">Debugging in WordPress (engl.)</a> (Diese Meldung wurde in Version 3.1.0 hinzugefügt.) in /var/www/clients/client31/web91/web/wp-includes/functions.php on line 4161
which roughly translates to
PHP notice: is_home was called incorrectly. Conditional query tags do not work before the query is run. Before then, they always return false. Please see Debugging in WordPress for more information. (This message was added in version 3.1.0.) in /var/www/clients/client31/web91/web/wp-includes/functions.php on line 4161
The same appears as a viariant with is_404 instead of is_home.
Looking up line 4161 in the file only reveals the bit of code that outputs the error message, not the code that causes it.
I hope that you can help us. Right now, our english site is missing a good bunch of its content and won’t save any newly entered values.