Should I be worried about this? Strange poos

Hello. Ever since I've had my rabbits, every so often, (every couple of weeks or so) I will find 1, kind of 'splodgey' poo in the shed. It's definitely not cecotropes, as I sometimes see them lying around too! I'm not sure which bun this is from either, but they are both very happy rabbits. I was thinking that maybe when this happens, its because they've overdone it on the grass that day! This may sound disgusting...but it's kind of like nutella!! :lol:
They have been checked out by the vets around 9 months ago, and are said to be in very good health. I am just not sure.

Could be their diet , how much pellets do they have , veg , treats , do they have tons of hay , 2 of my bunnys have these if I give them spring greens etc :wave:

They have loads of hay stuffed in a rack, and then some more in the litter boxes. Just before it gets dark they get 2 leaves of spring greens and a carrot to share, or a little bit of apple or pear. Thats about all they eat-they completely refuse any other leafy greens! Oh and the pellets-they get a handful a day each, and they don't normally finish it :lol:

Apple does this to Harry