Thanks for all the replies. Spoke location: rear, non-drive side. I am using a Delore Disc hub, but the tension is still lower on the non-drive side. Yes, I did re-use the rim and hub from a previous build, but there was no damage, I just re-built to use better spokes (DT alpine III). I thought about using eyelets/rivets, but that was this morning when I was thinking clearer. I have been pleased with the Rhyno Lite rims; the stock Mavic rims that came with the bike started to crack at the eyelet (prompting the replacement rims), so I am not too inclined to try Mavic again.

I think at this time I'll just keep an eye on it, and if I have some spare time I might replace the washer with a brass rivet/eyelet.