In Bedrock Edition, an undamaged brush can be used on an armadillo up to five times until it breaks. However, in Java Edition, it can only be used four times.
This may be due to the fact that tools can no longer reach 0 durability by normal means - increasing brush durability to 65 would fix this issue.
Seems more like a bedrock bug to me, considering the 0 durability thing. If anything, they could change how much the brush gets used by obtaining scutes.
Increasing the brush durability by 1 just to fix this seems silly to me...