1. Poor requirements and software specifications.
2. Software design.
3. Miscommunication between developers and testers.
4. Lack of domain language.
5. When time is short and also depends on poor coding.
6. Not proper knowledge on tools used if any.
adding few more to this is;
1. Improper deployment of the fixes made
2. Poor unit testing of the component by developer
3. Poor Integration testing within components
4. Manual errors
5. Communication GAP
6. Improper design (this is very important. if design is poor it may cause huge damage)
7. poor understanding of the specifications.
hello, In my opinion, Bugs are occurring from base things such as Requirement gathering, code review, code analysis, document development etc... if we control all these things then bug cost is very law if any new bug occur in live production, Thanks & regards