After moving my lansweeper from SQL Compact to SQL express there are 4 assets that are not up to date according to the report. When looking in Windows there those computers are up to date.
It is 3 Windows 10 1809 and one Windows Server 2016 1603. All other computers are showing up to date in Lansweeper, including W10 1809 and Ws 2016 1603.
That will be the issue then. The report will check which hotfixes are listed currently on the machine. If the KB of April's patch Tuesday isn't on there, it will lists it as not up to date.
The report doesn't check history to see if it was ever installed. Obviously just because it was once installed doesn't mean your machine is up to date at the moment either.
What you can do is use the combined patch Tuesday report next week once May has been added. That way even if it says it doesn't have the April update, you will see it does have the May update.
This is happening to me as well but only after the newest windows update. It appears if the computers have updated to the newest one the old month will show them out-of-date.
Have you gone over to the assets page and clicked the "Rescan Asset" button? This forces a full rescan of the assets, other scanning triggers do not always scan every single Windows item.
You can also check within Lansweeper whether it shows the KBs installed on those assets.