OK debug info below, not much in the way of an error, i can see it is trying to cache online image when kodi restarts but don't see anything after that in the log, it just stops writing. i checked the path in my browser and the image exists, i was following through the log as i was scrolling through my movie library, and it seems it doesn't always crash in this scenario, sometimes where the fanart.jpg is missing it successfully grabs and caches the image from the net, perhaps the problematic ones are large images? (the example is, filled my screen hi-res in Firefox)
17:16:46.855 T:3000797056 DEBUG: OnKey: down (0xf081) pressed, action is Down
17:16:46.858 T:3000797056 DEBUG: [Warning] CGUITextureManager::GetTexturePath: could not find texture 'OverlayUnwatched.png'
17:16:46.899 T:2990537536 DEBUG: CCurlFile::GetMimeType - http://image.tmdb.org/t/p/original/vdK1f9kpY5QEwrAiXs9R7PlerNC.jpg -> image/jpeg
17:16:46.900 T:2990537536 DEBUG: CurlFile::Open(0xcd21f68) http://image.tmdb.org/t/p/original/vdK1f9kpY5QEwrAiXs9R7PlerNC.jpg
17:16:46.926 T:2694839104 DEBUG: CCurlFile::GetMimeType - http://image.tmdb.org/t/p/original/bGpguMT9LtJXFeSietuX40mjfuu.jpg -> image/jpeg
17:16:46.927 T:2694839104 DEBUG: CurlFile::Open(0x111c4d30) http://image.tmdb.org/t/p/original/bGpguMT9LtJXFeSietuX40mjfuu.jpg
17:16:46.966 T:3000797056 DEBUG: Keyboard: scancode: 0x74, sym: 0x0112, unicode: 0x0000, modifier: 0x0
17:16:47.070 T:3000797056 DEBUG: [Warning] CGUITextureManager::GetTexturePath: could not find texture 'OverlayUnwatched.png'
17:16:47.970 T:2990537536 DEBUG: Caching image 'http://image.tmdb.org/t/p/original/vdK1f9kpY5QEwrAiXs9R7PlerNC.jpg' to '4/4ac0eafe.jpg':
it appears to be a combination of size of image and grabbing online, i manually saved the poster and fanart to the folder 3835x2160 and 2000x3000 respectively and didn't get any issue when scrolling to it through my library, Kodi cached them and displayed poster and fanart without issue