Yesterday I logged out with all my resistances at 75% or more.
Today I logged in and my fire and lightning are at 70%.
So fine I swap in a small idol for elemental resistance for 5%. What I swapped out was not resistance related.
Then it says those two are at 79%
I pull it out the idol I just placed in, and I am at 73% on those two.
It doesn’t make any sense.
Is anyone else seeing stuff, like this? Am I just missing something?
Some things will give resistance when certain conditions are met.
Something like character state.
But you also play offline, so resistance don’t matter. 
I don’t have conditionals that drop resistance, at least none that state it openly.
I don’t play offline, no idea where you got that from.
Some of your primary stats will also raise or lower resists
There’s just a 24 Forge Guard and a lvl 8 showing for release.
That I get.
But we are talking between logging out the night before and logging back in the next day.
No switching of gear or leveling in between.
Yes! I did see it happening with my armor, jumping between 54 and 64%. It was 64% before logout, and 54% after I relogged to the game, Im pretty sure some status are not properly removed from your character, so they are on your character until you re-login to game.
I wouldn’t worry about it too much, unless it starts happening with your 4 legendary potential items 
What do you mean it doesnt matter if he play offline ?