System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GTX 660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.59
Blender Version
Broken: version: 2.90 (sub 2), branch: master, commit date: 2020-05-21 21:20, hash: rB8f21f867e715
Worked: 2.79
Short description of error
Viewport starts to rerender from scratch even after click, grouping nodes, adding reroutes etc.
Here is comparision and details.