Sweet peas stems and no flowers?!

It's possible your plants are a bit late in flowering, but you can also ensure they'll flower by making sure they each got some rotted manure, something to climb up, and the end tips pinch to encourage lots of side bushing and flowers. Sweet peas seem to need to be growing vertically so they can throw out horizontal flowering shoots.

Trillium, I think the OP means that there are some stems with flowers but also some stems with no bloom developing on the end.
I noticed one of mine doing that yesterday.

Sheeesh. They ARE in flower and it is not too early. I have had them in flower by May the first!
Some stems are not developing flower buds, or unusually they are being eaten or taken. Thats the issue, not feeding, I never feed sweetpeas and have a bumper crop every year, what you do to, and put in the soil beforehand, is the food they need..

I picked off the tendrils one year, waste of time. Theory invented by someone with too much time on their hands !

Thanks for replies, after removing barren stems there doesn't seem too many now although there are still one or two.

This has never happened to me before so I was a bit unsure, generally looking good now! The spring sown ones are obviously a bit behind but hopefully they will keep flowering later on!