Referencing this Bug (reported multiple times already and often closed:
I am also experiencing this problem and have a file where it's showing up.
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: Quadro 5000/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 377.83
Broken: version: 2.83.3, branch: master, commit date: 2020-07-22 06:01, hash: rB353e5bd7493e
Notes on how to check this bug for yourself
I am currently running into this bug as well. It seems to be triggered when the strip in the layer above is moved.
I have created a quick scene to show the behaviour:
Steps to reproduce with the Scene:
Move the NLA Strip in the Layer called "Move This to the left" and watch the extrapolation mode on the strip below.
Here is the file in question: