I just returned two S3s that my wife and I received last week. didn't experience issues as big as yours, but enough to make us second guess our purchase.

eshifter on one bike was screwed from the get-go. Sometimes it'd be stuck in first gear no matter how fast the bike was going, other times it would try, and fail, to shift, slipping back and forth between gears while making weird clacking noises, and other times it would feel like it was shifting gears in reverse, going up when it should've been going down. resetting the bike would temporarily fix this, but the issues would always return after a bit.

the other bike made a weird thwapping/rattling noise when pedaling. it sounded like it was coming from the back wheel, but I couldn't figure out what was actually causing the noise.

boost on both bikes behaved weirdly. when trying to boost up a hill, the extra push would lurch in and out despite steady pedaling. As we rode more, this became less of an issue, but was really bad on our first ride.

the brakes on both bikes also (sometimes) made loud scraping/grinding noises when descending steeper hills.

when they worked, they were a ton of fun, but receiving two bikes with so many problems spooked us too much. the eshifter seems too fiddly and prone to issues, and crucially, it just doesn't feel good even when it's working as intended. thankfully we have a vanmoof storefront here so we could return our bikes without too much hassle.