Error when pickling - compiling project with 3.8.0-RC1

[OndrejSpanel]

My project fails compiling with 3.8.0-RC1. The error messages are quite cryptic.

Compiler version

3.8.0-RC1

Minimized code

Not yet, I will to provide it next week.

The type triggering the error looks like this:

  abstract class MapObject

  case class MapObjectInfo(name: String, obj: MapObject) {
    def isAgent: Boolean = obj.isInstanceOf[AgentRef]
    def isCrop: Boolean = !isAgent
    def isPlot: Boolean = obj.isPlot
  }
  type MapObjects = Map[(Int, Int), MapObjectInfo]

Output

error when pickling type (mapObjects : net.gamatron.procas.trpas.settlement.Settlement.MapObjects)
error when pickling tree this of class class dotty.tools.dotc.ast.Trees$This
error when pickling tree this.type of class class dotty.tools.dotc.ast.Trees$SingletonTypeTree
error when pickling tree this.type | pred.type of class class dotty.tools.dotc.ast.Trees$AppliedTypeTree
error when pickling tree new _root_.scala.annotation.retains[this.type | pred.type] of class class dotty.tools.dotc.ast.Trees$TypeApply
error when pickling tree new _root_.scala.annotation.retains[this.type | pred.type]() of class class dotty.tools.dotc.ast.Trees$Apply
error when pickling type Map[(Int, Int), net.gamatron.procas.trpas.settlement.Settlement.MapObjectInfo]

Expectation

The code should compile, or if it does not, the error should be actionable.