The problem is that none of my inserters can reach more than 1 tile--even for vanilla long inserters. This bug only happens when I am using top-left gui to adjust position. Hotkeys and per-inserter gui works fine, and the top-left gui can set pickup & drop position as expected. A brave new save also avoid such problem. I tried to clear & re-research related techs but the problem still exists. It may be some migration issue when install mods mid-game.
Here's what the bug looks like. Left inserter is what I get when setting location with top-left GUI -- distance is locked at 1. Right inserter is adjusted through per-inserter gui.

Here's my (heavily moded) save if anyone needs it to replicate this issue: https://drive.google.com/open?id=1p4cha ... G3PeG1yzQW