Tips for dealing with backlog?

There is no shame in resetting, considering you managed to work halfway through Wanikani in 6 months. Total reset, or resetting to a low level, like Level 3.

Wanikani teaches only vocabularies inclusive of all lower Levels’ Kanji, not only having the Kanji included; and this can potentially miss out couple of vocabularies that add up to Kanji’s readings and meanings.

Learning such way is probably doable considering having seen lots of Radicals and Kanji. This can be done with Yomichan+Anki, if Wanikani’s workload isn’t too overwhelming. I made this script a while ago and may help – [Userscript] WaniKani JJ External Definition from Weblio (JP) and Kanjipedia

In the past, I cut through no matter how big the backlog, with Reorder Ultimate, which also tells level remaining. However, currently Wanikani has the native feature (which might not be as good).; try using that feature can’t hurt.