You find good Information about Btrfs in the wiki
Did you check how full your btrfs is ?
Maybe you are near EOSPC ? Then btrfs will have a lot to do after an update 
Tip: Check how close you are to “out of space”. Look at Device unallocated: (not at Free (estimated): ) (Could not boot due to brfs no-space condition. How should I keep using BTRFS? - #7 by andreas85)