I have a similar issue. My motion+ wiimote has worked fine with sports resort, until it crashed mid-game the other day. Now, it always shows whichever wiimote is player 1 as not having motion plus, even though its built in.
The good news: I have found a workaround.
When you are on the player selection screen, where it shows the wiimote as not being motion plus. Disconnect the wiimote using alt+f5, connect a nunchuck, then reconnect (again using alt+f5), it should then consecutively register the nunchuck and motion plus. I think sometimes I have to disconnect and reconnect the wiimote more than once before it registers both the nunchuck and motion plus, but this is how I have been playing resort golf for the past week with my friends.
The good news: I have found a workaround.
When you are on the player selection screen, where it shows the wiimote as not being motion plus. Disconnect the wiimote using alt+f5, connect a nunchuck, then reconnect (again using alt+f5), it should then consecutively register the nunchuck and motion plus. I think sometimes I have to disconnect and reconnect the wiimote more than once before it registers both the nunchuck and motion plus, but this is how I have been playing resort golf for the past week with my friends.