Since this is only changing one of the products, please as a test, could you disable all non-WPML plugins, switch to the default theme and see if the problem persists?
This will help us know if there is any compatibility problem. If the problem is fixed, please, enable the plugins one by one to see if there is any compatibility problem between these plugins.
Hi, thanks for your answer. Of course it is not possible to turn off the plugins. The website is an existing one with a well running online shop. I can not take the entire page offline because of this error.
This is a bug that has already occurred with others. Years ago:
Yet it will be necessary to replicate this problem to see why this is happening. All the links you posted above (some very old ones) may not be directly related to the problem you are reporting.
Is it possible to replicate this in a testing environment? I'll need to request temporary access (wp-admin and FTP) to your site - preferably to a test site where the problem has been replicated if possible - in order to be of better help.
You will find the needed fields for this below the comment area when you log in to leave your next reply. The information you will enter is private which means only you and I can see and have access to it.
Note:
*** Please, can I install the Duplicator plugin (or All in One Migration) to make a copy of your site and install it on my test environment? This will help me debug the problem.