Park Assist issue

[Dunc77]

Hi,

I hope you can help, this is a complicated one to explain. The parking sensors on my 2015 A4 work but have a specific issue... when I start the car and select reverse, the park assist initialises, the proximity is displayed on the MMI and all looks fine. When I then select drive, the MMI still displays the proximity but no beeps. If I switch park assist off then on (still in drive) it starts beeping again. If I then select reverse, the beeping stops. If, at the end of a journey I select reverse, the park assist activates and beeps if there are objects around but if I want to park forwards, there are no beeps or proximity does not display on MMI. However, if press the park assist button it initialises. Both front and rear sensors work fine once initialised but I can't think what might cause this. Any ideas?

Thank you,

Dunc.