WebEngage Java Back end Developer interview questions

I was approached by the company on a Tophire. The interview process went very slow and took around 3 weeks and with a lot of rescheduling without any prior or post communication. The process had 4 rounds - 1st Round was a technical interview with a Software Developer, I was asked 1 Leetcode medium and a few questions on Java. 2nd Round was with a Team-lead, This again had a Leetcode medium question on arrays, I was able to solve it with 2 pointer based approach. There were a few dicussions on Java based topics, such as - ways to implement Singleton Class, Garbage Collectors, Memory spaces in JVM etc. I was also asked to give a low level design of a problem on building a file system. 3rd Round was with VP of Engineering, This was mostly a discussion on current works, responsibilities and a bit on interests and Tech Stack. 4th Round, This was an HR dicsussion Round, We couldn't have an agreement in terms of Salary expectations and I decided to not proceed further.