I'm still working through a significant backlog from the merger. None of our testing infrastructure worked with theirs, so I'm having to reimplement most of our test suites. We just got attachments back last week, after more than a year without them. Imagine diagnosing failures with the relevant logs missing(AI was actually quite useful here).
But, it's probably myopic to blame just that. Engineers suck at estimating task effort and I'm no exception. We've actually given up on assigning any estimate. So planning is just this kind of "yeah, that'll fit" guessing game.