Mockup feature isn't working

[ErinaIzzy]

I'm having a trouble with Mockup feature in Illustrator (Beta). It allows me to apply the effect but a waning sign that says 'The operation cannot complete because of unknown error [STEX]' popps up and the image and vector disappears. Does anyone know how to fix this? Please help!

[Monika Gause · Accepted solution]

I have experienced that myself. 

It would be important that you report this issue to https://illustrator.uservoice.com together with your hardware specifications and the Illustrator file, so that the engineers can work on it.