Digital OPK vs Original OPK

Chrissy
I know I'm ovulating or it's near I have those nasty pangs in left side of ovary, so I take a original clear blue and I have the two dark lines that idicate ovulation, I take the digital n I get the empty circle which means no lh surge did this happen to anyone else? I'm being monitored by my RE so I know for sure I'm ovulating.