Xperia C4 Marshmallow - weird problem

[vin97]

I upgraded my Xperia C4 (E5363) to Marshmallow using the Xperia Companion software. After the upgrade everyhting is fine except the bottom three buttons - BACK, HOME and RECENT APPS. They don't get clicked everytime I click them. Maybe only about once in 50 times. However it is NOT a hardware issue because when I rotate the screen horizontally and click on anything that appears in their place, they get clicked and the new three buttons don't get clicked. 

I tried the following -

1. Software repair to no avail

2. Reboot in Safe mode to no avail

I read about the "Wipe out cache partition" thing and really believe it could solve my problem. However I have no clue how to do that. Could somebody please help?

Vineet

[MarlonUk1]

try to perform a factory reset before and after the software repair using Xperia Companion

better if to use another pC or reinstall Xperia companion to make sure it downloads the update again.

Xperia devices doesnt have user accessible recovery mode, so wiping cache partition is not possible