I am having the same issue. Installed update on Monday and my hotspot hasn't worked since. It's very frustrating as I can not do any tasks on my laptop now as this was my only source of Internet.
Same issue here after the recent update this april. Hotspot button doesn't turn blue. I need to restart phone before I am able to turn hotspot on. If you don't do this right away after restart, after a while you won't be able to switch it on. Very annoying bug. Samsung, do you have this problem on your radar/working on it???