Does your UAT SSRS server have the webdings font installed?
That is the only time I've seen issues with fonts. We use barcode fonts in some of our reports and we needed to ensure the font was installed on the client machine (to render it to them) and on the SSRS server (to build the report with that font).
After installing the font, we needed to reboot the machine unfortunately. I've even seen it where just looking in the fonts folder caused the font to be "installed" and a reboot resolved the issue.
Since this is a UAT folder, I would check C:\windows\fonts and double check the font exists. If it does, try rebooting.
The above is all just my opinion on what you should do.
As with all advice you find on a random internet forum - you shouldn't blindly follow it. Always test on a test server to see if there is negative side effects before making changes to live!
I recommend you NEVER run "random code" you found online on any system you care about UNLESS you understand and can verify the code OR you don't care if the code trashes your system.