@mntuniman
If this is not a bug, or if any of this is helpful for your future reference... following are a few things I have learned/do in regards to my own uploads. I do not use Mods or CC, so this is how I work within the game's functionality/parameters:
(Also, I would assume the boulders you saw in your main screenshot were boulders that are on the lot or the adjacent lot and that the screenshot is being taken from a direction that is considered the 'street/main view' for the lot but not the side of the lot that you have built as the 'street/main view'. Unfortunately the game decides what is the 'street/main view' for each lot, and you will get used to how you can tell what view it will use. You cannot change the direction it will shoot from for the lot - it is preset - as far as I know.)
Unfortunately as far as I understand - and as I have experienced in my gallery uploads, you can 'select' the gallery pic by paging through options (click the camera icon) when uploading a household or room, but not with a lot. But when you save the lot you can see what the thumbnails will look like. Unfortunately the best option I have found is to 'stage' the lot as best you can. A few tips/things I have found to be helpful in this regard:
• In the gallery the screenshot is really important for catching anyone's interest. I will choose my lot (lighting direction and surroundings), time of day, season to best 'stage' the build. click 'save to gallery' (with or without actually saving it) to check how the thumbnails will look. When actually rolling out the final save before uploading to the gallery I even go to live mode at the right time of day and do a save at each hour close to the 'prime time' for how it looks and save to the gallery in 'Build' mode (the one you enter from 'Manage Worlds' not the live build mode) and compare them. The differences are subtle but the sun slowly moves, and after all that work why not get the best lighting you can? (Also, before each save in the edit mode I may place the saved lot again to make sure nothing was changed by the live sims.)
• Make sure your lot creates a thumbnail of the building from a front view.
• Do the 'change season' cheat to get to summer and wait for a non-rainy day.