So I'm not sure how this happens, but often with the autostep perk it won't limit me to stepping up a single block, and will instead jump me up to the top of ledges of any height (though if the jump is too far the server will usually rubber-band me right back to the ground for breaking the speed limit).
This will even jump gaps between blocks, occasionally leaving me on top of trees or similar should I step up a ledge underneath one.

It's mainly because it's written in a way to scale with other auto-step things like sash from botania or whatever, so you can 'stack' it. That also can lead up to letting you step up 3-4 blocks.

Now was this with only AS alone or in combination with other mods' step assist things? If it happens with only AS, can you provide maybe steps to reproduce this?

AS was the only step-assist active. I don't what triggers it, but it switches on or off at random if I die. I'll see if I can narrow anything down.

Well, if you can find the steps to reproduce this, that'd be amazing

Potentially fixed in the latest 1.12 version. Due to you and me not being able to consistently reproduce it, i call this solved.