IDE becomes slow when editing akka-http routing file

Hello, I wonder what could cause slow response of IDE's static analysis such as syntax highlighting and problems indicator when working with a Scala file containing akka-http Routes?

IntelliJ IDEA: 2021.2 #IU-212-4746.92

Scala plugin: 2021.2.15

Other non-bundle plugins installed: Eclipse Code Formatter (https://github.com/krasa/EclipseCodeFormatter#instructions ) but for other projects not for this one

Scala & sbt: 2.13.5 and 1.5.1

CPU Snapshot: uploaded as 2021_08_09_QrCtzbgbDShc8fyQ

When I try to edit one of the scala file containing akka-http routes, the IDE becomes incredibly slow - e.g. when you try adding a new Route like

  // inside of concat() - currently we only have 5 routes defined other than this one
  (path("test-api") & get) {
    // nothing yet, have to type
  }

then IntelliJ takes almost 10 seconds to evaluate that this route is invalid (returning Unit) and indicates the problem, and vice versa when I update the codes to something like:

  (path("test-api") & get) {
    complete("test-api ok")
}

What would be the solution for this issue? I don't see this much slow response from other scala files in the same project.