Other users have run into the same issue and, as mentioned above, Technical Support is aware. I am sure that it will be fixed as soon as possible.
Please be patient.
If you look through the forum threads, you'll see that some users have found a work-around by selecting different channels on their audio interfaces. For example:
garfy wrote:A number of users are posting about issues of which inputs on their interfaces are working in AT5. Hopefully, they are also opening tickets with official IK Support as well so it can be addressed.
I'm in the same situation, albeit with a different interface. Input 1 works fine but input 2 doesn't when selected as the left channel. However, in Settings in AT5 if I select input 2 as left channel and input 1 as right channel then signal comes through on channel 2. Hope that makes sense.