Are you using party synergies? Normally something like Guardian + Cleric + Blademaster + Arcanist with decent ratings would be enough to clear any of the early trials. The default orders should also be good enough to clear the early trials. Changing this up too much might be contributing to losing it.
Also, you can just withdraw or retreat from the trial. You don't have to finish it. The only thing that happens is you get a draw or loss on your league record, and then you get to move on. Taking an L is certainly better than losing your star party members.
If you can screenshot or send your party and trial info, we can get some better insight as to what's going wrong. For reference, I had a 10-1-0 record on the hardest difficulty, so you should certainly be able to beat your trials on the easiest difficulty.