>>1034593>Anyone have any ideas what could be causing this, how it might have happened, or any fixes?If you didn't clean the inside of your laptop, anything other than water will leave residue that causes corrosion over time.
Adding to what this anon said.
>>1034996Keyboards are wired in matrices. Pressing a key connects a row with a column. The processor then sends a signal through the column and measures which row it arrives in. If the circuit is damaged or destroyed at some point, all keys on the same row or column may stop working.
That explains why you have issues with your Fn and Z key (same row as arrow keys) and Pg Dn (same column).
You can try opening the laptop and cleaning the PCB with 90%+ isopropyl alcohol or distilled or deionized water and cotton swabs or a soft toothbrush (unused). If you're lucky that fixes the problem. In the worst case the damage is permanent and you'll need a new keyboard.