Great idea on the ova size. I just took over support for PI in our environment. In fact I didn't even have access to the app until this morning so it is all new to me.
One note is that it was working - just like yours - up until yesterday when the NullException popped up. I am on a call with the WLAN engineer who was/is working on it now so this was new information to me that it had worked previously until yesterday.
Please keep me updated and if I open a TAC case I will also update you on Ciscos response.
I have a few tasks to complete this morning before I am free to open a TAC case but I will be opening one ASAP once I finish up my configuration tasks.