Issue with none translatable fields

Hello wc-qTX team,

I am experiencing an issue, first I want to say that I am not totally sure that it comes from the wc-qTx plugin but there are some points that make me think it is.
First, I show you the errors I get :

Warning: strpos() expects parameter 1 to be string, array given in .../wp-includes/shortcodes.php on line 205
Warning: preg_match_all() expects parameter 2 to be string, array given in .../wp-includes/shortcodes.php on line 213
Warning: array_intersect(): Argument #2 is not an array in .../wp-includes/shortcodes.php on line 214
Array

(the string Array is displayed with the others error lines)

So, there is a field in page options called “Custom titlebar content” which is not translatable but which was already filed before I install the plugin.
When I delete the textual content and I save the modification, I get the errors shown above. Sometimes, the string Array is displayed alone (I mean without the warning error lines) BUT it is prefixed with one of the 2 language names (I don’t know if it is linked but it is the wordpress install language).

In order to try to make the errors disappear, I came back to the first revision, reload front and it works… But the point is, as soon as I save it again (even not making any change), the errors are back. The 3 lines errors if I am not lucky, ‘(language) Array’ if I am displaying the original wp language or just ‘Array’ if I am in english language.
As it was not working, I decided to fill it with raw multilingual format, I saved it but coming back to the field, I realised that some brakets had been added with non-sense:
what I added : [:fr]FR[:en]EN[:]
after saving : [:fr][:fr]FR[:en]EN[:][:en]FRENFR[:]

Have you ever heard about that issue. What could I do?
Thanks for helping!