Protected Content – All Pages Blank

I have an odd issue that cropped up on a live client site this afternoon. Everything has been running smoothly until now.

As of this evening – the site is displaying “blank screens” for all pages. There are a small number (5 or 6) pages and bbPress that are protected behind PC. Again – this has been working properly. This evening all pages on the site are blank.

I am able to log in to Admin and after a bit of testing have determined that deactivating PC, seems to resolve the issue (pages display normally), but obviously with PC off the content we want to protect is no longer protected.

I have gone through the PC setting to see if the client has changed any setting. All appears to be normal. BUT – if I enable PC – the front facing pages all go blank – nothing is displayed. Very odd. No new plugins have been added recently (so I don’t see this as a conflict).

I have enabled SUPPORT ACCESS and would really appreciate it if someone could take a look. For now – I have turned PC off – turning it on will make the issue return.

Edit to Add: Admin log-ins are abel to see all the pages normally, you need to be logged out of Admin to see the white screens.

Thanks in advance for any assistance.