I have seen so many problem like this every day, when you drop something In water after dry it it still corroded in side try opening the phone and clean the complete mother with 99% alcohol and dry it with hot air gun hope every thing will be fine
To find out this problem you can try this step try replace a wiring lcd back metal plate the connected to the home buttons, if still same remove the home button and carefully remove the home back two small plate which take click clean it and put it bank and check