I've only put 35 miles on my bike since installing a BBSDH mid-drive. At first, I didn't see any major issue but on my last ride (20 miles on a paved bike path) I started getting rapid chain skipping under load in the 1st and 2nd highest (smallest) gears. I've worked on re-indexing and setting the H-limit screw but nothing fixes it.
I don't see the skipping in the 3rd and 4th highest gear and the 2nd highest is REALLY bad-bang, bang, bang. I worked on the bike today, starting from scratch with setting up the indexing. Everything is fine in the bike rack. It's shifting completely. But as soon as it's under load in PAS 3 (out of 5) it will barely pedal without the banging of the skipping gear. I guess it's skipping over the top of the 2nd gear on the cassette but I can't really see it.
I stopped pedaling and just used the throttle and still it's bang bang bang as the chain is yanked over the gears.
The 9-sp cassette has less than 200 miles on it. The chain is only a month old. The first ten miles were trouble free.
I have the Lekki narrow/wide 46T chain ring and I used 2mm of spacers to clear the chainstay during the build.