For reference just updated from the official 2018 version (2018.4.23f1) to 2019.3.7f1.
The full error is:
Assets\AstarPathfindingProject\Core\RVO\RVOCoreSimulator.cs(805,13): error CS0433: The type ‘ManualResetEventSlim’ exists in both ‘System.Threading, Version=1.0.2856.102, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ and ‘netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51’
This error also exists a second time with:
Assets\AstarPathfindingProject\Core\RVO\RVOCoreSimulator.cs(806,13)…
Re-importing Astar seems not to help this issue. What might be causing this and how can I fix?