I'm having a strange problem. On some sheets, there are certain layers I couldn't make visible. Everything worked fine on the model.

• If I make the viewport active and look in the layers manager, it says 12 total layers, displayed 12 even though some are hidden.
• If I click on Show all layers, The missing layer doesn't appear.
• Nothing is frozen or locked AFAIK.
• If I choose Hide Layer then click on a entity. I can never seem to make that entities layer visible again except...
• I finally figured out that I can click on Layer Preview, select all, Unclick both check boxes, then press the preview button. This seems to bring the layers back.

This is awfully confusing. Why is it so easy to hide a layer and so hard to show it again?