Hello Ivo,
I opened an issue with Gantry 5 a few days ago regarding a bug, and after this morning modified it, and opened a new one with J2Store. I tagged you in a response in the Gantry 5 issue, but wanted to make sure you were aware of them since you have the Delight template.
https://github.com/gantry/gantry5/issues/3199
https://github.com/J2Store4/j2store4/issues/46
The "Title" gives a basic description of the issue.