Armor Stand cannot be targeted via a custom name

I am attempting to target a random armor stand by a particular name, and then setblocking a redstone block at that armor stand. This is my attempt at a Random Output generator. 

I've been getting said armor stand with a command block, by using:

/give @p minecraft:armor_stand{CustomName:"Random"} (with quotations, without them, neither works)

and then attempting to target it with this:

/execute at @e[name="Random",limit=1,sort=random] run setblock ~ ~ ~ minecraft:redstone_block replace

This does not work, for some reason. I suspect this is a bug rather than a deliberate gameplay element because this works with other entities, such as slimes. About the only entity I can't get this to work on is the armor stand, which is the only entity ideal for what I'm trying to do.