What are these clearings in Amazon rainforest?
Hard to say. Some could be clearings for log landings, some for small villages or outposts used by the military or others, some cleared due to natural disturbance in the area (e.g. fire from lightening strikes) though I'd expect the latter to have sparse canopy and not be totally clear.

Many of these patches don't have signs of good access routes (other than by air or through thick vegetation). No doubt there can be smaller trails and rivers under the canopy, but we don't see any substantial routes with canopy cleared overhead. Therefore, logging and mining seems less likely, though both occur in the region. Smaller scale operations, like a clearing for more sun-loving plants by a local human population, could account for some of these though.

On the village or outpost possibility

Consider these clearings:


Two relatively nearby clearings, one with what appears to be grainy rocks but could be thatched roofs of a village
Another nearby clearing that appears to have a significant amount of its soil covered in a darker shaded texture, again perhaps thatched roofs
And another clearing, partially open and partially with this same darker texture to it in a shape that could certainly be a spread of small buildings in a community


I searched for on-the-ground views of potential villages and found a few that could match the view from above.

Here's a large communal structure in a clearing which could match some of the textures we see. Some indigenous groups of the Amazon live in large structures like this as a community, and some just use large structures like this as ceremonial communal spaces.


Here's a set of buildings in a village clearing. Note how close the forest canopy comes to the buildings. Given how thick the forest is, it's probably not easy to manage, but that could be all the more reason to get to bare ground in these village clearings.


Here's a pretty amazing example of small scale clearings and manipulation of the forest landscape by indigenous communities. While we're not seeing this from a satellite, it points out how the lack of texture nearby and between these clearings doesn't necessarily mean there's no trails or human presence. It appears these structures are surrounded by unusual tree canopies - perhaps banana or another agroforest crop - which could be cultivated from nearby shelters. 


In conclusion, a likely possibility is that these clearings are signs of relatively-isolated small-scale villages or outposts.