The usual diagnosis here
Post bolts loosen as the rim joist cycles wet and dry; under tree cover, add moisture held at the post base. If tightening no longer holds, the wood being clamped has gone soft — and that's worth catching now, while it's a section repair rather than a deck-edge rebuild.
Next step
Each loose post at its base, the run from the side, a short video if the post rocks — through the form for a range.
Railing mechanics: see the service page. City rules: see the Menlo Park page.