I was using Enigma yesterday to send a few transactions but it wasn't consistent.

The first tx went using 3, the next using 5 expired and so did the following TX i tried to make. But then the next one using 5 went.

There were 25 nodes online. What holds up or allows Enigma transactions to expire? Is it lack of nodes?

And how does another node accept/validate an Enigma transaction, is it automatic or does the user have to 'okay' it?