I often forget a line or two of some song I've written while practicing or rehearsing. That's normal. Happens to the best of us.
Occasionally I can't remember the lines after I've had time to sit and think about them. That's more annoying, but they'll generally come back to me if I put the song aside and try again later.
Tonight, during rehearsal, while playing a song we hadn't touched for over a year, I found that I couldn't remember the melody for the bridge.
Yeah, it's time to think about rotating our set list more often.