Can't scroll from the left and top side of the frozen line on iPad

Steps to Reproduce

1. iPad (iOS 14 tested) + Chrome 
2. go to http://10.1.3.45:8089/keikai-demo/excel_like
3. Keikai version: 5.6.0-SNAPSHOT dated 2020/12/23
4. click on Liquidity sheet
5. put your finger on the left side of the frozen line and scroll, it won't scroll up/down
6. same if you put the finger on the top side of the frozen line, it won't scroll either

(found this issue when testing Keikai-386. however the behavior is slightly different, in iPad it never succeeds, whereas in Keikai-386 desktop browsers, it succeeds for the first time)

Current Result

it doesn't scroll

Expected Result

it scrolls

Debug Information

Workaround