Fields not appearing in Metrics -> Sum -> Field drop-down

I have a new index for which I'm trying to create my first dashboard, but I cannot select any of my fields! The only field I can see is log.offset.

I am specifically expecting to see a field called rx_bytes or rx_bytes.keyword, which appear to be Searchable and Aggregatable.

Where should I look to troubleshoot why this, and other fields, are not appearing in my aggregation options under visualizations? This appears to be specific to Sum Aggregations, even though I have this working for a similar dashboard on a different index.

edit > Also, it appears to be aggregatable under "Buckets > Terms".

edit > Continuing to dig, I found that this field defaults to a String instead of a Number for some reason. Looking into how to change defaults. Also, I do not see Number as an option for me to rename this field. In the other dashboard, the field name is packet0.length and this is a Number that is aggregatable.

The index pattern is based on what your elasticsearch mapping contains- if your mapping of these fields is as string fields, Kibana will treat them as strings. If you've reindexed your data or changed your mappings in elasticsearch, you can refresh your kibana index pattern and it will pick up those changes.