Nightly builds can be incorrectly named if the build lasts into the next day
Some people on reddit have reported that the Lineage updater shows the 'Install' button on updates that have already been applied.
Most likely the issue is with the naming of the updates being wrong. I assume that when a build lasts past midnight into the next day it gets named after the new date.
So for example: build starts on 01.06. but lasts until 02.06. and thus is named 20200602 during the upload.
This causes some confusion for the updater. Mine for example shows I'm on the 01 June build but since the update file is named after 02 June it still shows the 'Install' button.
Screenshot attached of my updater: