The main problem I've seen with OKRs in a technical setting is that they haven't accounted for steady state support, or sudden urgent issues.

Both of those make up important work that has to be done in a timeframe shorter than the OKR reporting period.

As a result important work goes untracked, and completeness of KRs are affected since people had to focus on "unexpected" issues instead.

A compounding effect is burnout because a persons OKR workload and review process doesn't accurately reflect the day-to-day work that they did. Heroics are needed to avoid people higher up the management ladder seeing unfinished work under your name.