I'm assuming you are in Bridge's Output module and you are creating a PDF (not called contact sheet anymore).
I'm running OSX 10.9.4 and Photoshop CC (2014.2.1) 20141014.r.257 x64, Bridge 126.96.36.199.
I selected 8 images in Bridge and clicked on Refresh Preview. The initial filename Overlays were tiny.
Set Font size to 14 then 24 then 48 and did a Refresh Preview after each, and the filenames got bigger and bigger with no problem in the resulting PDF document.
That was with the default Arial Regular font.
Compare your app versions to mine above.
jml - Thank you for your note. I'm not using Bridge. Contact Sheet II in Photoshop itself is what I'm using. Not creating PDFs either, some adjustment is always necessary plus I add my logo and job info block before sending proof sheet to the client. Output is jpeg so I can work on it. I'll keep my fingers crossed that some other user out there has a remedy. Thanks again.
If you have not used Bridge's Output module, it has a lot more features. Besides making PDF contact sheets, it also makes WEB Galleries.
The Bridge CC Output Module has to be downloaded from Adobe and installed. It was removed from the CC distribution for some reason.
Instructions and download at link below, for PC and MAC.
Please use the below link to install the CSX2.1 Contact sheet version in Bridge.
It contains a Pdf along with the steps on how to rectify the issue.
Please reply if you face any issue in following the steps mentioned.
Thank you for posting on Adobe Forums.
GautamBahl - thanks for your note. I spotted the earlier user with same problem as I've had and have been following instructions in the SourceForge link. I've been testing it and it works. A little more tweaking and it'll be as good as new. Problem solved. Thank you, thank you!