I tried loading a Structure (a smelting system by JL2579) into my testing world using Structureblocks after making an error and having to alter the Structure file, after copying it into my test world and loading it again this Glitch happend, see Screenshots (the other screenshot show how it's supossed to look)
To recreate this glitch do the following:
1.Save the two Structure files you can find attached into your worlds structure folder, if you dont know how either dont bother or look it up on yt/google (it takes like 10 seconds)

2.Get a Structure Block in that world
("/give @p minecraft:structure_block" but you should know that)

3.Load the two Structures in the order Glitch1 then Glitch2.
(when loading Glitch2 about a double chest of coal may spill out because I dont know, sooo... sorry?)

4.Look at the front and the Hoppers should be glitched out, they work as normal and breaking them or closing and reopening the world fixed the Glitch.

EDIT: I used the smelting system as the Structures(Glitch1,Glitch2) because I couldn't get it to work with another structure I made to demonstrate the Glitch so I used the smelting system instead.