I had a similar experience a couple of times. The first time, the feeling of burnout wasn’t so bad, and I was able to just slowly plug-away at the reviews (holding off on adding any new lessons until I was back to a reasonable daily review rate), but the second time I spent too long away and even though I was level 28 at the time, I couldn’t remember most of the kanji from level 10 up. So, I reset to level 7. Wrote a quick write up about it back then if you’re interested: After a long absence, I reset (to level 7), and I’m glad I did.
Also, since then, I’ve decided to stop trying to finish WK at some arbitrary fast pace (playing the SRS game, so to speak) and just focus on enjoying learning Japanese through WK at a gentler, more comfortable, and ultimately more sustainable pace. I found this thread for like-minded WK folks: 
Let’s Durtle the Scenic Route 
, and I enjoy the little ‘philosophy’ or whatever you want to call it behind it, and there’s some good tips and tricks in there as well for how to use WK in a way that’s most enjoyable for yourself. I’ve even posted a couple of the tricks I use in there as well. They’re easy and don’t require any user scripts, just the built in WK features. Not that there’s anything wrong with userscripts! I used to use them a lot. But I had to start on a fresh computer recently and didn’t bother to take the time to install any scripts. Still it’s pretty straightforward to ‘take the scenic route’ with the ‘no frills’ option. 