I have the VS 2019.
When I build a solution, I get some compile errors in "BuildOnly" mode. However, when I fix several of the errors, I expect the Error List to refresh, but is not the case: I still have the fixed errors in the list, till the next re/build.
I should rebuild the solution to get the list updated. What is the cause and solutions of this VS bug?
I saw people say to remove the .vs file, but should I do that every time I need to update the ErrorList? Why it's not performed automatically?
It depends on which tool is providing those error items, and how it's triggered. Some tools only run on file save, or when invoked explicitly by some gesture.
In the case of the C# compiler, it should be running a design-time build (your scenario is even mentioned in the documentation's signs of failure). You might try the steps further down that page to try to diagnose the issue.