Blank screen when going to checkout (only in English site), MySQL issue?

-- HikaShop version -- : 3.1.1 business
-- Joomla version -- : 3.7.5
-- PHP version -- : 5.6.26 / 7.0.3
-- Browser(s) name and version -- : Firefox 55.0.3 (applies to other browsers, too)
-- Error-message(debug-mod must be tuned on) -- : Notice: Undefined offset: 1 in /home/cskman12/www/cskmanagement.com/Joomla/plugins/system/cachecontrol/cachecontrol.php on line 74

Notice: Trying to get property of non-object in /home/cskman12/www/cskmanagement.com/Joomla/administrator/components/com_icagenda/utilities/events/data.php on line 45

Fatal error: Call to a member function get() on null in /home/cskman12/www/cskmanagement.com/Joomla/administrator/components/com_icagenda/utilities/events/data.php on line 45

I have a bilingual website with a Hikashop webstore that has been working properly for a while.

But now, customers are getting a blank screen when going to the checkout, after having put their items in the basket.
However, this only happens in the English version of the shop. If customers use the German version, it is all fine, and they get to the next step (entering their address etc.).

I suspect that there is somehow something wrong with the mySQL database because when I go to the HikaShop configuration page, running the "check database", I am getting the Error "1064 You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'LIMIT 1' at line 1".
Also, when I try to install HikaShop 3.2 business (currently 3.1.1 business), I am getting a similar error:
Warning
You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'LIMIT 1' at line 1

I have alread checked this:
www.hikashop.com/forum/product-category-...your-sql-syntax.html but it seems, in my current HikaShop version, this is already corrected.

Any idea?

Thanks a lot in advance
Chris