Hi there,
I have been using Libreelec for some time now and always used to only use the offical releases (for wife acceptance), however since Inputstream I started using the alphas, but unfortunately it looks like after all the updates my system has been getting a bit unstable. I am also using the offical kodi rpi3 case (for heat related questions!).
Unfortunately I sometimes get reboots of the RPI3s, but unfortunately don't get a Crash Log 
But I can say: When it happens, the Skin resets (All Menu Items are back to default, e.g. I disabled "Music Video" which gets re-enabled). I think it might be runtime or heat related and want to ask, how I could try to pinpoint it down and fix it.
I have been trying to pinpoint the problem, so this is what I did/tried to come to the conclusion:
- I disabled a few addons (TV Headend Server/Client and Webgrab Plus) - since the problems started with beta 2 ( when I also started to use Webgrab Plus). With the Addons disabled everything was good again, so I re-enabled them one by one and with everything besides Webgrab Plus it works ok for 2 weeks. When re-enabling WebgrabPlus I got 3 Reboots in 2 days... So I thought it was an Addon Issue and tried to get help there and disabled it again.
- Yesterday I loaded some vacation images (~10mb per picture) on the hard drive attached to the rpi and tried to open them - which gave me reproducable ways to get the rpi rebooting! Thats why I started to think it might be either some runtime related issue (many pictures to load) or some issue with accessing the data from the usb drive - or due to heat ( I have got a warning icon sometimes).
2 other things happen sometimes (usually before system is getting unstable): Icons fail to load (or it take for ever to load ...) and sometimes the "clicking sound" becomes way off from what it usually is... I have no idea if this is connected, but I thought every information might help 
Could you please help me!?!
Thank you,
Linkin
edit: just to be sure: I am not using any illegal addon. I am just using addons from Kodi/Librelec and Kodinerds Repo + Amazon Addon (from Sandman Repo)