This is related to some sort of stability updates.Minor changes of system.It's not a security patch as it have old Feb security patch.

What is the behaviour of mobile phone after update?Did it get slow down or any other problem?

Switch off 'Fast Charging' and see it solve your problem or not??Go toSettings _Battery and Device care_ Battery_More battery settings _ Fast charging...If it solve your problem then it means you are charging your mobile in hot environment as fast ch...

Sub standard USB cables & chargers make the phone charging slow due to not compatible with the phone.Qualcomm Quick Charge 2.0 standard charger & cable from any genuine brand will surely solve your issue...

For 1 & 3 problem factory reset might solve the issue.For 2, this is not the problem.It's a safety feature of android which switches off the screen or mobile to prevent the battery exhausting which leads to the battery damage.