I asked around and as far as I can tell this is a bug.
I've been losing hhps while logged in, logged out I lose none, for the past 3ish days.
I have shoes, its not leeches or black FEPs, no one or no thing is attacking me I'm not losing shp but hhp, it would appear to be around 1-3 an hour.
I died recently, and had over 300% travel weariness easily at one point, those are really the only relevant things I can think of tbh