I have a some what similar stint. Worked at a start that got acquired by big co for the product and customers, although not the product my team was responsible for. Our product got quickly put on maintenance mode with promises to rewrite the whole thing at some point.

So by that point I had been working there for a year and some, knew the system pretty well and we had pretty much nothing to do. No new features, very few bugs due to little change in the product.

I'd show up to work at 10, leave for lunch for 2+ hours, and leave the office at 4. And even then I was mostly surfing the web and chatting with friends most of the day. The rest of the team and my manager knew, but they also knew there was actually no work. We'd all go play badminton before lunch some times and so there were 3 hours periods where no one was around.

Was pretty nice at first. Steady pay, no responsibilities or stress. But quickly got really boring. And since it was my first job out of school, not very good for learning and growth. Ironically the slow pace also really dampened by motivation to look for another job, so I hung around probably a year longer than I should have.