1). Search boxes not visible on mobile and tablets. This is a CSS issue. Most likely Kentico removed some of the harcoded css classes or renamed them. I'd debug your CSS and see what you find.
2). After every upgrade (major or minor) you need to resign the macros. Check the documentation for how to do this.
3). I'm willing to bet this is a similar formatting issue as #1. Debug your css and see what has changed. From v7 to v8.x styling and overall layout of the OOTB controls has changed considerably for the better.