Comment 1 for bug 1927791

Thank you for taking the time to report this bug and helping to make Ubuntu better. Please execute the following command only once, as it will automatically gather debugging information, in a terminal:

apport-collect 1927791

When reporting bugs in the future please use apport by using 'ubuntu-bug' and the name of the package affected. You can learn more about this functionality at https://wiki.ubuntu.com/ReportingBugs.

From your description this reads like a duplicate of issues that occur at the greeter or `sddm` which is not unique to Lubuntu, however without a picture I cannot confirm this.

Please check out https://bugs.launchpad.net/ubuntu/+source/sddm/+bug/1865837 and if it matches, please say so, or mark this report a duplicate of that report (there are others too that also fitted this description, but that is a like radeon card..)