Giving a CustomName to an entity in the form of a JSON array with two or more objects causes the last JSON object in the array to be duplicated.

When applying the following JSON

[{"text":"1","color":"#f73c20"},{"text":"2","color":"#f73c20"}]

To an entity with the following command

/summon minecraft:armor_stand ~ ~1 ~ {"CustomNameVisible":true,"CustomName":"[{\"text\":\"1\",\"color\":\"#f73c20\"},{\"text\":\"2\",\"color\":\"#20a8f7\"}]"}

Produces the following nametag