Why do bugs our developers “fixed” keep coming back?
It depends on which kind of bug keeps coming back, because each has a different cause and a different cure. Nearly every bug is an unforeseen side effect of another change, a change that was misunderstood, or a plain mistake. A bug that returns after a fix usually means the team patched the symptom and never asked which of the three it was.
Evidence
I wrote about this in Software bugs: Focus on what you can control. Nearly all bugs come from one of three causes, and each calls for a different response.
Unforeseen side effects. A change breaks something else that nobody expected it to touch. These are nearly unpreventable, and they grow with the complexity of the software: every feature and every custom branch adds more ways for one fix to undo another. The response is to find the root cause, then reduce the complexity, refactor, or add automated tests so the same break is caught before it ships.
Misunderstood changes. The developer built what they thought was asked for, not what was meant. These are entirely preventable. The response is better communication and tracking between the people who ask for a change and the people who make it.
Plain mistakes. The developer simply got it wrong. Some of these can be prevented. The response is to work out why the mistake happened and whether a safeguard exists that is worth its cost, so the same mistake is not made again.
I build my own software with that discipline written into the process. In WASBuilder, every ticket gets a specification before any code is written, and if anything is unclear the agent asks first rather than guessing, which is aimed squarely at misunderstood changes. A separate review then checks the branch against the specification and acceptance criteria, and sends it back if it falls short. Nothing reaches production until a human approves the merge. Each ticket keeps its specification, plan, tests and review report in plain text, so when a bug does come back there is a record of what the fix was meant to do.
What it takes
The bug history. Your issue tracker, or whatever stands in for it, including the bugs that were closed and then reopened.
Access to the code and the people. The repository and its tests, and time with the developers and with whoever writes the requests they work from.
A willingness to change how changes are asked for, checked and approved. Most repeat bugs are a process problem, and better developers alone will not stop them.
The honest limits: side effects never go to zero in complex software, and sometimes the right answer for an old, tangled system is to fix the bug cleanly and move on. An audit says which bugs are worth preventing and how, but it does not fix them. Your team does that, or a Fractional CTO engagement does.
Next step
Tell me which bugs keep coming back. The Software Project Audit is a fixed-price investigation that traces them to their cause and tells you plainly what to change first.