My days generally consist of some mixture of working on code, investigating issues, and attending meetings. Meetings dominate my Tuesdays (and usually only Tuesdays, thankfully), and the remainder of the week is split between debugging and coding. Issues identified generally become coding work, e.g., writing up a design doc, pushing a quick hotfix to a PR branch, or adding passive health check logic to keep errant hardware out of our clusters.
Digging into the issues requires a bit of detective work. The research impact varies from the vague (“my job seems to be running slower than it was yesterday”) to the terrifyingly specific (“I think if I push more than 30Gbps over the Ethernet NIC, I cause a kernel panic?”). This is likely a familiar mix: productive on days that proceed as expected, and exciting when the expected is disrupted and you get the chance to learn something new.