I've been in exactly the same situation as you. For me it happened because I was in a miserable team and company that didn't do anything significant or properly. I was constantly left without work and bored so at that point I stopped caring and was just getting away with any work.
What I did however is to use this free time to work on personal projects and to prepare for interviews for other companies. This played out nicely as I later changed job to a much more interesting company and team where I can make important contributions to the work and I care doing a good job.
Sounds to me like you are in the same situation, meaning you are not mentally stimulated and you simply don't care. My advice is either change job or if this is not an option then use this time to work on personal projects or further develop your skills/hobbies. Basically make sure you don't waste your time and put it into something productive for future gains.
What I did however is to use this free time to work on personal projects and to prepare for interviews for other companies. This played out nicely as I later changed job to a much more interesting company and team where I can make important contributions to the work and I care doing a good job.
Sounds to me like you are in the same situation, meaning you are not mentally stimulated and you simply don't care. My advice is either change job or if this is not an option then use this time to work on personal projects or further develop your skills/hobbies. Basically make sure you don't waste your time and put it into something productive for future gains.