Something strange just happened. I tried to spin a Pokestop right as it was turning to blue, but it wouldn't let me.
I impatiently kept trying and eventually it said 'try again later'. So I restarted my game and now the Pokestop is purple! But the other ones around me (I'm in an area where I can reach 4) are able to be used perfectly.
Did I lose my items?
Look at your diary and you will know if you got your items or not. Sometimes i've the same issue and i always get items.
Pokestops turn from purple to blue over a few seconds - but the colour change completes a bit before the pokestop is fully ready - if you spin it just after it completes turning blue the animation does not show the items nor does it turn purple again - but if you spin it again it says 'Try again later' as a purple pokestop does. Then a few seconds later it goes purple and behaves like a recently used pokestop. However if you review the journal it shows that you do get the items even though you don't see them on the screen as you are spinning the pokestop.
It only means the 5-minutes timer from your last spin hasn't completed yet. You have to wait some more until 5 minutes had actually lapsed before you can spin again.
