Hard to start after shut down bateen 10 t0 30 mins

My 2007 camry with 282k miles is hard to start after turning off engine between 10 to 30 mins. It has no problem to start first in the morning and after turning off engine 30 mins later.

I almost read post here everyday. I know 5w20 always does well maintenance for his vehicles. I have never changed transmission fluid,  break fluid. But this car is still working well.

History  of problem maintenance :

LR wear baring and out tie rod

4 spark plugs and 2 coil packs, O2 sensor 

front and back stabilizer links

alternator

This camry used to have engine oil consumption problem. Later Toyota provided warranty  and changed 2 pistons, now the engine runs very well.

I check online and ask one good mechanic, but no one can give exactly why I have hard to start problem. Most possibilitis are:

collant level sensor problem, collant temperature sensorproblem , crankshaft sensor problem, spark plugs problem, etc

But nobody can tell exactly problem is.

Anybody can give suggestions? 

Thanks.