I had the same issue with mine. Low fluid due to a leak. Probably allowed air into the lines. Filled mine and over a little time it worked itself out.
Just an fyi...if your box is bad be ready for a shock to the wallet (especially if you have the work done). Aftermarket box when I priced them were about $450, factory even more....labor will be in the 4-6 hour range.
Check your fluid level first! The fitting on the hoses are a prime area of leaks on our VXs and most other vehicles.