Trailer bearing grease issue

2 of my 4 trailer hubs grease has become fairly liquified and purple leaning towards black rather than red. 

I have what I'm pretty sure are Dexter ezlube spindles on my trailer. The little rubber plugs on the dust cap had dry rotted so I replaced them a couple weeks ago. When I did this I also pumped out as much of the old grease as I could and replaced it with new, as there had been some water intrusion. I used the Lucas red and tacky grease which is what was in them to begin with. The bearings were replaced and packed with the Lucas so I'm pretty sure I don't have a dissimilar grease issue. I've heard since that particular grease is not best for this application but I had no issues last season.  

I pulled a 600 mile round trip

last week and checked the hubs for excessive heat when I stopped for fuel and didn't detect any but clearly there's something going on with those two hubs. Any thoughts or advice are appreciated. Everything I know to check without tearing them down is as it should be other than the grease condition.