Q.What is eating my Swiss chard?
I have planted several lots of Swiss chard. Some get to a stage where they can be planted out. Carefully planted some out under wire mesh
And some slug pellets. They got eaten overnight. Kept some in the greenhouse but they all got eaten. Pretty sure it’s not slugs or snails and no evidence of anything else. Nothing else is affected. Any suggestions please

Certified GKH Gardening Expert
It's not clear if your chard's leaves are being eaten or if the entire plants are being eaten. If you've ruled out insects, aphids, beetles, caterpillars and other such creatures, the only thing I can think of that can get under wire mesh would be rabbits, squirrels, chipmunks, voles, moles or other less adorable burrowing rodents. Look for some holes in your soil.
Here are a couple articles that may help:
https://www.gardeningknowhow.com/plant-problems/pests/animals/vole-control.htm
https://www.gardeningknowhow.com/plant-problems/pests/animals/garden-mouse-control.htm