How to reproduce:
1. Create an HDRP template project
2. Create a "Lit Shader graph" e.g.
3. Create a "Swizzle Node"
4. Observe in the drop-down lists for color, only "Red" is available

Expected result: Drop down lists should show Green, Blue, Red as options
Actual result: Only Red is shown

Reproducible with: 10.3.2 - 11.0.0 (2020.3.0f1 - 2021.2.0a3)
Couldn't test with: 12.0.0 (Swizzle node is changed, channels no longer can be picked from a list)

Notes:
- If you close the Graph and re-open it again, all the channels are listed
- If you modify the values of the Swizzle Node via other nodes e.g. "Vector 4", the Shader graph is repainted and it shows all the channels
- Reproducible with URP and HDRP