Which log I should look to see reason for server crashes? 
I got logs in log folder and in oxide folder.

[SERVER v1.0.24] Console: BetterChatFilter.cs(150,22): warning CS0114: `Oxide.Plugins.BetterChatFilter.LoadDefaultMessages()' hides inherited member `Oxide.Core.Plugins.Plugin.LoadDefaultMessages()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword
C:\Rust_Servers\My_Server\Oxide.Core.dll (Location of the symbol related to previous warning)
ProximitySystem.cs(53,14): warning CS0114: `Oxide.Plugins.ProximitySystem.LoadConfig()' hides inherited member `Oxide.Core.Plugins.Plugin.LoadConfig()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword
C:\Rust_Servers\My_Server\Oxide.Core.dll (Location of the symbol related to previous warning)
ProximitySystem.cs(87,14): warning CS0114: `Oxide.Plugins.ProximitySystem.LoadDefaultConfig()' hides inherited member `Oxide.Core.Plugins.Plugin.LoadDefaultConfig()'. To make the current member override that implementation, add the override keyword. Otherwise add the new keyword
C:\Rust_Servers\My_Server\Oxide.Core.dll (Location of the symbol related to previous warning)
AutomatedEvents.cs(21,60): warning CS0649: Field `Oxide.Plugins.AutomatedEvents.AlphaChristmas' is never assigned to, and will always have its default value `null'
AutomatedEvents.cs(21,76): warning CS0649: Field `Oxide.Plugins.AutomatedEvents.FancyDrop' is never assigned to, and will always have its default value `null'
AutomatedEvents.cs(21,87): warning CS0649: Field `Oxide.Plugins.AutomatedEvents.PlaneCrash' is never assigned to, and will always have its default value `null'
AutomatedEvents.cs(21,99): warning CS0649: Field `Oxide.Plugins.AutomatedEvents.RustTanic' is never assigned to, and will always have its default value `null'
AutomatedEvents.cs(21,110): warning CS0649: Field `Oxide.Plugins.AutomatedEvents.HeliRefuel' is never assigned to, and will always have its default value `null'
AutomatedEvents.cs(21,122): warning CS0649: Field `Oxide.Plugins.AutomatedEvents.PilotEject' is never assigned to, and will always have its default value `null'
BetterChatFilter.cs(20,42): warning CS0169: The private field `Oxide.Plugins.BetterChatFilter.BetterChat' is never used
BetterChatFilter.cs(43,36): warning CS0169: The private field `Oxide.Plugins.BetterChatFilter.offensedata' is never used
ProximitySystem.cs(50,29): warning CS0649: Field `Oxide.Plugins.ProximitySystem.ProximityData.date' is never assigned to, and will always have its default value
TimedExecute.cs(24,15): warning CS0169: The private field `Oxide.Plugins.TimedExecute.ptimer' is never used
​

Could be anything really. Do you got complete list of plugins? How many entites or players do you have? What does your host say about this? Alot of times on cheap servers the server crashed because it rans out of ram, so what are your specs. You could always ask your host if they know.

The log you provided was only the compiler log, which as you can see only contains warnings, not errors. You would need to check your actual log files. Also note that a server shutdown is not necessarily a crash; crashes would generate crash dumps in your server install location generally.