**System Information**
Operating system: Linux-5.3.0-59-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce GTX 1660 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 435.21
**Blender Version**
Broken: version: 2.90.0 Alpha, branch: master, commit date: 2020-06-14 17:09, hash: `rB4155f8dc21a9`
**Short description of error**
In the material panel the material slot will not show a preview if that material was added on frame lower than 2
11ba9eec70175b39e34943c8ffacb54c35cbb897 is the first bad commit
**Exact steps for others to reproduce the error**
1. Open Blender and select 2D Animation on the Splash Screen
2. If you are on frame `0` or `1` add a new Material Slot and Create a new Material. => //there will be no preview//
3. Go to a `frame >= 2` and add a new Material Slot and Create a new Material. =>// there will be a preview (even if it takes a few seconds to update)//
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