Hello DS, 

I am using a free version of Draftsight  and having issues with viewports. I have 19 viewports on a sheet and some of them lose function. The view disappears (so it just looks like a rectangle with nothing in it). When I select it, the properties window states it is a viewport, however I can not double click inside if it. If I select and delete it, then undo the delete, the viewport comes back as works as expected. If I save, close and reopen the viewport is empty. If I switch to model view and come back to the sheet the viewport will be empty. Looking at print preview, it also shows empty view ports. 

There are just a few viewports that are doing this. I have tried copy-paste, creating new ones, moving them so there is a gap between the ports, shutting down background programs...any ideas? Is there a limit to how many viewports you can have? File size? it seems to be ok around 13-14 viewports, but once you start adding more than that they start dropping out. File size is 292KB. 

Draftsight 2015 SP3

Win7 64 bit 

Intel i7 

6gb ram

running about 60% of memory