Vanishing boards

I spent a day creating an extension to a new layout. An industry, the track, points and signals were put in place across three boards. I saved the revised layout, then reopened it to find that the additional boards had vanished or become invisible but that the industry and trackwork were still there, floating on a sea of white. The rest of the layout was fine. This is not the first time it's happened; I assume I must have saved the game in he wrong way. Does anyone recognise this and know of a recovery procedure? I'm not touching it until I can either fix it or accept that the work has to be redone.

Grab a texture.
Click as if to add the texture to your invisible baseboard.
The baseboard should reappear.

If it does, then it's a corrupted texture somewhere.

If you don't want to ruin your original route, try this on a clone first and see if it works. I haven't had this problem in sometime, but I spent quite a lot of time weeding out old textures one day.