Ubisoft have added a bunch of balancing and mechanics changes to the Rainbow Six Siege test server recently and they will apparently be coming to live servers as a part of Operation Burnt Horizon once it launches on 06 March 2019.
Rainbow Six Siege aims to be a tactical shooter but the lean spam has led to some people calling it a lean simulator. One of the reasons this happened is likely because the feature may have been better than intended - it allowed some operators to peek behind corners without revealing themselves. Ubisoft are looking to tackle this issue by changing the placement of the player camera when leaning, even when at "full lean" position.
Apparently, the developers have also streamlined their animation changes which should allow them to edit animations easier in the future. In fact, one player-requested change has already been implemented - sprinting operators will not lean their head forward as much, making the sprint animation feel more natural. There is currently no indication on how this might impact hitboxes.
This addendum to the Operation Burnt Horizon will balance out Dokkaebi and Capitao as well. Dokkaebi's gadget was deemed to be too annoying for too long so the phone buzzing time has been cut down to 12 seconds instead of 18. Naturally, these numbers only apply if you don't stop to turn the phone of yourself.
Capitao's fire bolts have also turned out to be a mess that was seen as overpowered. Back during the Wind Bastion days, his bolts didn't have as much radius, meaning he couldn't cover as much area and deny as many pathways to the defenders. His bolts are subject to further changes as the official post indicates the developers are not sure themselves what they want to do with them in the future.
There are plenty of bug fixes, but one caught our eye in particular. Caveira's Luison was recently nerfed with lowered damage and higher recoil, but apparently, it started shooting slower as well. Scary skull ladies shouldn't feel as meagre after the update as Luison will be back to its fire rate.
You can see the entire wall of text that describes the fixes on the official Burnt Horizon Addendum post.