When I open a svg in inkscape a black box appears over the image, and zooming I usually makes it disappear. Additionally sometimes selecting over the region makes the box disappear. I have the latest version of inkscape, and have reinstalled it already. Running Ubuntu 18.04. Finally, the biggest nuisance is that upon exporting to a png, large black bars appear horizontally across three regions of the image. Any suggestions would be much appreciated, thanks so much in advance.

How big is the file and how much ram installed?

Also which installer for inkscape?

I have the same issue.

File size is 1,841 KB.  RAM is 4 GB.  OS is Windows 10, used MSI installer. Version is 1.01.

Task Manager shows 215.9 MB used by the Editor.   Help>About Memory is shown in attached img.

Any suggestions pls?

In the case of converted pdfs, there are often many clipped objects, that when un-clipped have a black rectangle the size of the document. These can be deleted without issue.

In the case of very complex images (usually converted from pdf) there can be corrupted objects that have zero dimension (or astronomical dimension) that will not properly render (display), causing black regions depending on zoom factor. These can be hard to locate, except by process of elimination. 

Hi Tyler, thanks, I remembered that from your previous advice. However, unlike last time, I cannot select the black box at all.

Oh well, perhaps it's a corrupted object as you suggested... I can live with the zoom factor at greater than "fit page in window".  SVG attached.

I think there might be a problem with clips, or clones?  Again from what you'd said previously, I did Object>Clip>Release in a zoom view where I could see the diagram.

Got the black box - from the Status line, it said it was a "Clone". Tried deleting it, but didn't appear to work.

It might have, there might be quite a few stacked exactly on top of each other (sometimes dozens). Clones can be deleted the same as any other object.

Yes, I found that out when I had a look at the XML editor... must be a couple of hundred all up! Mind you, there are 3 "sets" of objects, 2 and 3 are modified copies of 1 (LHS)...

I persisted and deleted all the clones in the 3rd "set" (diagram on RHS) then copied just those objects to a new doc. Same prob when I zoomed out though, going to check this new doc out some more.

Hi Tyler, finally found the culprit, it was a rectangle, rotated 90°, with a gradient fill. 

In case any tech guys at Inkscape want to perhaps recreate it, I've attached an img showing it's XML.