Q.meyer lemon trees
I have several Meyers lemon trees. Last year one had about 50 lemons on it. It is planted in ground and although covered it lost most of leaves, the one right next to it did not lose leaves and now has lemons on it. This one has lots of leaves and new limbs, and also has one really long branch that looks different from rest, smaller leaves and longer thorns. Should that branch be cut out? Why is this one not blooming and making lemons?

A sprout or sucker branch should be removed from the tree.
Loss of leaves and lack of fruit can be caused by various issues.
These links will help you pinpoint the issues.
https://www.gardeningknowhow.com/edible/fruits/lemons/growing-meyer-lemons.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/learn-about-fertilizer-for-a-lemon-tree.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/thorns-on-citrus-trees.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-leaf-drop.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-not-fruiting.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-pruning.htm
https://www.gardeningknowhow.com/edible/fruits/citrus/leaves-falling-off-citrus-tree.htm
https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1455.pdf