Another "add to cart not working" Topic

-- url of the page with the problem -- : www.samwelsupplies.com
-- HikaShop version -- : 3.2.1
-- Joomla version -- : 3.
-- PHP version -- : 3.8.2
-- Browser(s) name and version -- : All

Hello Hikapeople,

I have searched trhough all the other topics, but none seem to have had the answers that would fix the problem I am finding here.
On the website, a logged in user is able to add products to cart. Then, expected is that the cart in the top right will update. At this moment it only does so after a page refresh. The minicart in top does function well otherwise, proceeding to checkout etc seems to work fine.

I have thusfar tried the following solutions:
- Change template to protostar - Changed back because no effect
- clear all customizations in "view tab"
- Set caching to off
- changed session handler
- installed Jeasy
- Switched the notify plugin on and off
- changed popup box mode in the configuration
- changed around positions of the cart

So far to no avail. I do want to mention that add to cart did work fine at some point, giving a nice little popup in the top right corner. I do not know at which point it got broken ( I must have been changing something in the website ) I just got notified by an attentive customer that the webshop was "not working right" ..
Right now I am back to the legacy mode as this is actually functioning ( looks nowhere as slick as the new popup though!)

Are there any other ideas what could be going wrong?