I solved the issue by creating a new product with the same settings and variants.
The problem occurs with all orders of these specific variant-combinations. also in different products.
Summarized, the following combinations are available for product 1:
Sex: hen, rooster
Size: XXS, XS, S
Variant: Left, Right, Pair
The problem occurs every time, size XXS oder XS is selected. For size S its working fine.
The same problem occurs with product 2:
Sex: hen, rooster
Size: M, L, XL
Variant: Left, Right, Pair
Here the problem occurs every time, size M oder L is selected. For size XL its working fine.
So the pattern may be, that the 2 smaller sizes cause the error, the third size does not.
System report: https://pastebin.com/KJqNghgY
