Font checkers will check to see if there are errors, but can not determine if there is a conflict with Photoshop.
Think back and see what has changed since it last worked. Did you add software, fonts, or harware?
Do you use Suitcase for fonts? There have been some with confilcts with this program.
Did you reset your preferences? A reinstall will not affect this file.
Your system log viewer is your friend. Mac apps are pretty talkative and your system will log any critical errors...
Thank you both for your responses!
I later found that it was one file that was causing the issue. Not entirely sure what I had done to make that file behave that way but I've tested Photoshop and have not been able to replicate the issue.