Delphi 10.4.2 delivered important fixes to the LSP and Code Insight. In general, everything is working well for me. However, I can still produce the dreaded red squiggles:

As you can see compilation was successful, but Code Insight and Structure View are broken.

In this case, the problem is a result of updating the Library Path in Options.

Some 3rd party components do not configure library paths for all of the compilation targets. When I switched to Android64 I received a compilation error, the source file was not found. Simple fix, in Options I just added the path for Android64 and hit rebuild. That’s when the above issue occurs.

Just restart the IDE to get rid of the problem.

I believe this issue can also be solved by forcing the LSP/Code Insight to refresh when certain options are updated, such as the Library Path.

I hope this tip helps.