Membership Plugin - Creeping Whiteout Issues

Hi, I installed 'Membership' and I've been gradually building up the pages/site but then pages started to go blank/White.

It appears to happen more frequently when using my 'Visitor' setting.

More and more pages are now going blank though and I'm not sure what to do? I tried deactivating the plugin, logging out & reactivating but still the same.

Any ideas? I've granted support access.