Column Not Found

edited 12/09/19 in Smartsheet Basics

Hello! When I am filtering down information from a sheet into multiple reports, a few of my columns are labeled as 'not found'. I haven’t renamed the columns, which I understand could cause this -although on one of the columns I changed the column type from 'symbols' to 'text' fairly recently (but not for my other one). 

This has happened before previously and I wrote it off as a glitch because eventually it did show back up. While I can go back and re-select the column again from report builder, I have 200 reports linked with this sheet and it is a bit of a pain. 

If anyone has any insight as to why this might have happened and how to prevent it in the future I would greatly appreciate it.

Thank you.