Basically, Inkscape will sometimes start opening dozens of errors, mostly with the following message:
You need to install the UniConvertor software.
For GNU/Linux: install the package python-uniconvertor.
For Windows: download it from https://sk1project.net/modules.php?name=Products&product=uniconvertor&op=download and install into your Inkscape's Python location
Unfortunately, the package
python-uniconvertor is not available for 18.04, and appears to have been dropped after 17.10.
The only way to continue working is to
killall inkscape and reopen. The problem doesn't seem to happen while Inkscape is the active focused window; it only happens when I switch virtual desktops or Inkscape is hidden behind other windows.