I have three space stations that use stock solar panels and a lander on the surface of Minmus that uses two Near Future MX-0 generators. During warp (never higher than 7), the stations update their EC usage nicely, but the lander never updates. I read that generators should also work in background.

If I turn off the background processing, both the solar panels and the generators work the same way, using estimation and catch-up. If I enable it, only the solar panels generate EC. The only workaround is to put a lot of battery on a ship and make it active before lack of EC harms Kerbals.

Sorry I'm not familiar with this mod. Out of the box. TAC LS works with any part/part mod using the stock generator module. My guess is this mod does not.
I looked at Near Future mods but I couldn't find the MX-0 generator. Can you please supply a link to the mod you are using thanks.

I'm also having this issue. It looks like it is because NFE uses FissionGenerator for its nuclear reactors.

This has now been added.