Something doesn't add up -- increased job experience yields decreased readiness for interviews

A year ago, I was confident in my interview skills. I had been doing prep courses online, CTCI, hackerrank, etc. It paid off because I landed a job as a software developer. However, since then I've be

A year ago, I was confident in my interview skills. I had been doing prep courses online, CTCI, hackerrank, etc. It paid off because I landed a job as a software developer. However, since then I've been focused on my job, and thus the CTCI/hackerrank skills are fading. Now that I have some experience, I have been approached by a couple companies for interviews. However, I went to one and completely bombed the technical portion. This seems contradictory... shouldn't interviewing be easier now that I am an experienced developer? Not to mention that as time passes, the general knowledge/skills I learned during my CS degree are fading... How do experienced devs handle this conundrum? My gut reaction is to turn down any interviews until I've had some time to brush up my skills. Also, I'm thinking that when I do want to actively pursue a new job, I will need to resign from my current job to study, do practice problems, etc, as opposed to looking for a new job while still at my current job. How do other experienced devs handle this?