Yep; mojo comes and goes, it's a fact of life I've come to terms with long ago. You have to, or otherwise you'll soon burn out completely. The hard part is not beating yourself up over not being productive.
I tend to paint every mini I start to the best of my abilities, which means that progress is quite slow. But I can live with this.
My personal problem with not getting any painting done, is not as much lack of mojo, as a lack of energy. I blame it on me getting older, and jobs becoming ever more demanding. Also, being a parent certainly is draining too!
When I was still flying solo, I could basically paint every night of the week. Not to say I did, but I could. This gave me a lot of freedom, and not painting one night because I wanted to go out, or watch a movie, or even just lounge and do nothing was not a big deal; plenty of evenings to do so when the mood struck.
But then I got into a (new) relationship, got married, and eventually became a father, and each of these steps, as incremental as they were, siphoned off available time to paint. To the current point where missing the one night a week I have available for painting (next to actually gaming, RPG-night, the gym, quality time with the wife and daughter, social commitments etc) has a huge impact on my output.
Because all of a sudden, it completely destroys my output when I don't feel like picking up a brush on that one night I actually have the opportunity to. As a consequence, I almost feel guilty for not painting at that time, because I tend to set goals for myself in regards to my yearly painting output, which get hit hard if I don't regularly paint.
See; I want to paint 100 28mm miniatures (or equivalent) per year (in 2021, I made this number for the very first time! Yay me

).
I also found that I'm not as much feeling guilty about not being productive, as that I regularly find myself slightly irritated with the fact. Often, my lack of painting is caused by me being thoroughly exhausted after a long day of working, making dinner, doing the dishes, and then working through the loooong bedtime ritual of the little lady

And by the end of this, I'm finally free to do what I want, but I'm too tired to do anything but sit and watch a series or a movie (but often there's too little time in the evening to watch a full length one).
So I used to be able to paint whenever I fancied, but now, with so much other commitments, the stars must align just right for me to be able to get some painting time in. And even then I can get frustrated because I can't get enough done in one sitting. And this can also completely kill my mojo.
But eventually I found that re-arranging the lead mountain, tidying up my gaming room, prepping projects, or even just planning hypothetical projects during those energy-sparse evenings have their merit as well, and can actually be satisfying too.
Forcing yourself to do something productive and hobby related each day, even if it's just 10 minutes or half an hour doing the things above also helps feeling good about the hobby in the long run. Sometimes I just stand for 5 minutes looking at my display cabinets, thinking of how to expand the collection(s) within, and even those moments are valuable!
The important part has been repeated over and over in this thread, and it very much holds true; it's just a hobby and don't beat yourself up over not being able to perfectly make use of the allotted time. Just enjoy those moments when it all comes together
