Burnout happens. It isn't just a Battletech thing, of course, but any fandom. I have my interests outside of Battletech ebb and flow depending on what's going on. For me, the only fictional universe I enjoy more than this one is Fallout- and while there's been some great developments from that the past few years (the board game is surprisingly good!), a few years ago things were rough on that front. I'd played the older games to a point that they were almost muscle-memory, there was no sign of movement beyond wild rumors on 'Fallout 4'... it was tough to maintain an interest. Battletech has been pretty quiet the past couple of years, certainly compared to the days of the Jihad and War of Reaving books giving us a ton to discuss and absorb (which is NOT to say that the products are lesser in quality per se, just lesser in terms of quantity!). I admit my own interest has waned as a result- still here, still painting miniatures, still coming up with game ideas... but not as gung-ho as I was in, say, 2012. Hoping that changes again soon.
But hey, other factors weigh in too. It's hard to maintain that interest level when real life beats on you. Long work hours can do it, or a new kid in the house, etc. can all factor in- less time for hobbies means less time with it on the mind, and that means it's further and further from your thoughts in-general. Maybe another game takes your attention- I know I'm an avid Star Trek Attack Wing player, for example, and my paint bench regularly shoves Battletech aside in favor of working on a Vulcan ship or something like that (and vice versa, to be fair).
Best thing to do? Don't fight that burnout feeling. Let it happen- don't read Test of Vengeance or paint an Orion because you're a Battletech fan and want to fight that feeling of burnout. Walk away for a bit- those books and such aren't going anywhere. Enjoy other things, deal with what life throws at you, and if the urge comes back, then follow it back to the Inner Sphere. And you know what? It might never do so. You may just call it a career, hang up the neurohelmet, and be done with the game. That happens too, no shame in it.
The important thing, do what's right for you as a fan rather than force something you don't really want to do- THAT will lead to you going past 'burnout' and heading into 'chore' territory.