product variant selection causes ajax ploblems

Hello,

i have a problem with the product variant selection after the new update from Oxid CE 4.5.11 to 4.6.8. Each selection throws an error in the oxajax.js "Uncaught TypeError: Cannot read property 'debuginfo' of null" and after that it will not update the choices (size, color) and the buy button remain always disabled. Does anyone knows this problem?

Thx,
DC