when a villager with trades  has armor on (iron in this case) you cannot open a trade window.  it closes immediatly.. 
also you cant tell if its wearing armor (shoudl ahve at least an iron belt and shoe buckle and headband or soemthing)  or matchign leather/.diamond band and be able to hold appropriate tool. shears book etc

(have to use commands to see if wearing armor and sometimes only it will tell you teh truth)
armor was injected onto villager with dispenser. 

standard java 1.14.3 server not spigot (though spigot has less lag because worlds are separated by end/nether/overworld etc)