Forms missing in Backend after update 3.12.x

We recently receive a notice that the Visforms forms were no longer displayed in the administration after Update to Visforms 3.12., although the forms were working fine in the frontend.

The problem occured, because on the website the akeeba admin tools were used to set the collation in the database for the website. If you use this feature, please make sure, that you run the "set collation" routine after Joomla! Updates, Component Installations or Updates again, in order to make sure, that all tables have the same collation and can be joined savely.

Joomla! has decided to use the utf8mb4_unicode_ci if the database does support this collation.
Joomla! automatically checks on every update, if the databsae does support this collation and if it has already tried to convert the tables (this information is stored in the database)
If it has not already converted the tables, it tries to convert the table and then stores the "tables are converted" information in the database.
I have basically adopted this mechanism for Visforms.
When I looked at the database (were form display was not working in the administration), I could see, that there was a wild mix of different collations.
utf8mb4_unicode_ci, utf8mb4_general_ci and utf8_general_ci
Especially the Joomla! core tables mostly had the utf8mb4_general_ci collation, although the stored information was, that the tables were converted to utf8mb4_unicode_ci
Therefore an sql error occures, because Visforms tries to link information from the Joomla! user table to Visforms table and that did not work properly because of the different collations and no form records could be selected from the database.

Aicha