Dear BarbRC,
Good day! Thank you for posting your query in our community.
Based on your description, when you try to change style in SharePoint List column conditional formatting, icons don't work properly. I tested it on my side, and I could reproduce the same issue as yours.
Since we can reproduce the same situation as yours, the best way to troubleshoot the issue is to report the issue to the related Team. So we suggest you contact the administrators in your organizations and open a support ticket in the Office 365 admin center via the steps in the article for further help. The engineers in related team have higher permission and more resource than us to help check it from background and collect the log remotely.
Your understanding and patience will be highly appreciated.
Sincerely,
Jazlyn | Microsoft Community Moderator